Force measurement system

ABSTRACT

A force measurement system is disclosed herein. The force measurement system includes a force measurement assembly configured to receive a subject thereon, and one or more data processing devices operatively coupled to the force measurement assembly. In one or more embodiments, the one or more data processing devices are operatively coupled to the force measurement assembly, the one or more data processing devices configured to receive one or more signals that are representative of forces and/or moments being applied to a top surface of the force measurement assembly by the subject, and to convert the one or more signals into output forces and/or moments, the one or more data processing devices further configured to predict one or more balance parameters of the subject using a trained neural network.

CROSS-REFERENCE TO RELATED APPLICATIONS

This is a continuation-in-part of U.S. Nonprovisional patent applicationSer. No. 16/870,987, entitled “Force Measurement System”, filed on May10, 2020; which is a continuation-in-part of U.S. Nonprovisional patentapplication Ser. No. 16/571,103, entitled “Force Measurement System”,filed on Sep. 14, 2019, now U.S. Pat. No. 10,646,153; which is acontinuation-in-part of U.S. Nonprovisional patent application Ser. No.16/297,615, entitled “Force Measurement System”, filed on Mar. 9, 2019,now U.S. Pat. No. 10,413,230; which is a continuation-in-part of U.S.Nonprovisional patent application Ser. No. 16/025,321, entitled “ForceMeasurement System”, filed on Jul. 2, 2018, now U.S. Pat. No.10,231,662; which is a continuation-in-part of U.S. Nonprovisionalpatent application Ser. No. 15/713,166, entitled “Force MeasurementSystem”, filed on Sep. 22, 2017, now U.S. Pat. No. 10,010,286; which isa continuation-in-part of U.S. Nonprovisional patent application Ser.No. 15/365,325, entitled “Force Measurement System and a Method ofTesting a Subject”, filed on Nov. 30, 2016, now U.S. Pat. No. 9,770,203;which is a continuation-in-part of U.S. Nonprovisional patentapplication Ser. No. 14/797,149, entitled “Force and/or MotionMeasurement System and a Method of Testing a Subject”, filed on Jul. 12,2015, now U.S. Pat. No. 9,526,443; which is a continuation-in-part ofU.S. Nonprovisional patent application Ser. No. 14/474,110, entitled“Force and/or Motion Measurement System and a Method of Testing aSubject Using the Same”, filed on Aug. 30, 2014, now U.S. Pat. No.9,081,436; which is a continuation-in-part of U.S. Nonprovisional patentapplication Ser. No. 13/958,348, entitled “Force and/or MotionMeasurement System and a Method for Training a Subject Using the Same”,filed on Aug. 2, 2013, now U.S. Pat. No. 8,847,989; which is acontinuation-in-part of U.S. Nonprovisional patent application Ser. No.13/904,751, entitled “Force Measurement System Having A DisplaceableForce Measurement Assembly”, filed on May 29, 2013, now U.S. Pat. No.8,704,855; which claims the benefit of U.S. Provisional PatentApplication No. 61/754,556, entitled “Force Measurement System Having ADisplaceable Force Measurement Assembly”, filed on Jan. 19, 2013, thedisclosure of each of which is hereby incorporated by reference as ifset forth in their entirety herein.

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

Not Applicable.

NAMES OF THE PARTIES TO A JOINT RESEARCH AGREEMENT

Not Applicable.

INCORPORATION BY REFERENCE OF MATERIAL SUBMITTED ON A COMPACT DISK

Not Applicable.

BACKGROUND OF THE INVENTION 1. Field of the Invention

The invention generally relates to a force measurement system. Moreparticularly, the invention relates to a force and/or motion measurementsystem and a method for testing a subject using the same.

2. Background

Force measurement systems are utilized in various fields to quantify thereaction forces and moments exchanged between a body and supportsurface. For example, in biomedical applications, force measurementsystems are used for gait analysis, assessing balance and mobility,evaluating sports performance, and assessing ergonomics. In order toquantify the forces and moments resulting from the body disposedthereon, the force measurement system includes some type of forcemeasurement device. Depending on the particular application, the forcemeasurement device may take the form of a balance plate, force plate,jump plate, an instrumented treadmill, or some other device that iscapable of quantifying the forces and moments exchanged between the bodyand the support surface.

A balance assessment of a human subject is frequently performed using aspecialized type of a force plate, which is generally known as a balanceplate. In general, individuals maintain their balance using inputs fromproprioceptive, vestibular and visual systems. Conventional balancesystems are known that assess one or more of these inputs. However,these conventional balance systems often employ antiquated technologythat significantly affects their ability to accurately assess a person'sbalance and/or renders them cumbersome and difficult to use by patientsand the operators thereof (e.g., clinicians and other medicalpersonnel). For example, some of these conventional balance systemsemploy displaceable background enclosures with fixed images imprintedthereon that are not readily adaptable to different testing schemes.

Therefore, what is needed is a force measurement system having a forcemeasurement assembly that employs virtual reality scenarios and/orsimulated environments for effectively assessing the balancecharacteristics of a subject and offering much greater flexibility inthe balance assessment testing that can be employed. Moreover, what isneeded is a method of testing a subject that utilizes a forcemeasurement system employing flexible and interactive virtual realityscenarios and/or simulated environments. Furthermore, a force and motionmeasurement system is needed that includes an immersive visual displaydevice that enables a subject being tested to become effectivelyimmersed in a virtual reality scenario or an interactive game. Inaddition, a force measurement system is needed that is capable ofdetermining whether a measurement error is present. Also, a forcemeasurement system is needed that is capable of determining a balancestrategy of a subject disposed thereon.

BRIEF SUMMARY OF EMBODIMENTS OF THE INVENTION

Accordingly, the present invention is directed to a force measurementsystem that substantially obviates one or more problems resulting fromthe limitations and deficiencies of the related art.

In accordance with one or more embodiments of the present invention,there is provided a force measurement system that includes a forcemeasurement assembly configured to receive a subject, the forcemeasurement assembly having a top surface for receiving at least oneportion of the body of the subject; and at least one force transducer,the at least one force transducer configured to sense one or moremeasured quantities and output one or more signals that arerepresentative of forces and/or moments being applied to the top surfaceof the force measurement assembly by the subject; and one or more dataprocessing devices operatively coupled to the force measurementassembly, the one or more data processing devices configured to receivethe one or more signals that are representative of the forces and/ormoments being applied to the top surface of the force measurementassembly by the subject, and to convert the one or more signals intooutput forces and/or moments, the one or more data processing devicesfurther configured to predict one or more balance parameters of thesubject using a trained neural network.

In a further embodiment of the present invention, the one or more dataprocessing devices are further configured to provide feedback to thesubject regarding his or her balance based upon the one or morepredicted balance parameters of the subject determined using the trainedneural network.

In yet a further embodiment, the one or more balance parameterspredicted by the one or more data processing devices using the trainedneural network comprise at least one of: (i) a center of pressure, (ii)a center of mass, (iii) a center of gravity, (iv) a sway angle, and (v)a type of balance strategy.

In still a further embodiment, the force measurement system furthercomprises a motion capture system comprising at least one motion capturedevice configured to detect a pose of the subject on the forcemeasurement assembly, the motion capture system being operativelycoupled to the one or more data processing devices.

In yet a further embodiment, the at least one motion capture device ofthe motion capture system comprises at least one camera configured tocapture the pose of the subject, the camera being operatively coupled tothe one or more data processing devices; and the one or more dataprocessing devices are configured to determine the pose of the subjecton the force measurement assembly based upon output data from the atleast one camera.

In still a further embodiment, the one or more data processing devicesare further configured to determine the pose of the subject from theoutput data of the at least one camera by utilizing the trained neuralnetwork.

In yet a further embodiment, the one or more data processing devices arefurther configured to determine a plausibility of the pose of thesubject on the force measurement assembly by using the trained neuralnetwork.

In still a further embodiment, the force measurement assembly is in theform of an instrumented treadmill.

In yet a further embodiment, the force measurement assembly is in theform of a force plate or a balance plate.

In still a further embodiment, the force measurement system furthercomprises a base assembly having a stationary portion and a displaceableportion, the force measurement assembly forming a part of thedisplaceable portion of the base assembly, and the force measurementsystem additionally comprising at least one actuator operatively coupledto the one or more data processing devices, the at least one actuatorconfigured to displace the force measurement assembly relative to thestationary portion of the base assembly.

In yet a further embodiment, the at least one actuator comprises a firstactuator configured to rotate the force measurement assembly about atransverse rotational axis and a second actuator configured to translatethe displaceable portion of the base assembly that includes the forcemeasurement assembly.

In still a further embodiment, the force measurement system furthercomprises at least one visual display device having an output screen,the at least one visual display device configured to display one or morescenes on the output screen so that the one or more scenes are viewableby the subject; and the one or more data processing devices areconfigured to dynamically adjust one or more visual elements in the oneor more scenes displayed on the output screen of the at least one visualdisplay device based upon movement characteristics of the subject.

In yet a further embodiment, the one or more data processing devices arefurther configured to quantify errors in one or more balance tasksperformed by the subject on the force measurement assembly.

In still a further embodiment, the one or more balance tasks includedual tasks where the subject is standing on the force measurementassembly while simultaneously performing a task using his or her upperbody.

It is to be understood that the foregoing general description and thefollowing detailed description of the present invention are merelyexemplary and explanatory in nature. As such, the foregoing generaldescription and the following detailed description of the inventionshould not be construed to limit the scope of the appended claims in anysense.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

The invention will now be described, by way of example, with referenceto the accompanying drawings, in which:

FIG. 1 is a diagrammatic perspective view of a force measurement systemhaving a displaceable force measurement assembly according to anembodiment of the invention;

FIG. 2 is a perspective view of an immersive subject visual displaydevice, a base assembly, and displaceable force measurement assembly ofthe force measurement system according to an embodiment of theinvention;

FIG. 3 is a perspective view of an immersive subject visual displaydevice and a cutaway perspective view of a base assembly anddisplaceable force measurement assembly of the force measurement systemaccording to an embodiment of the invention, wherein several covers ofthe base assembly are removed;

FIG. 4 is a diagrammatic perspective view of one force measurementassembly used in the force measurement system, according to anembodiment of the invention, wherein the force measurement assembly isin the form of a dual force plate;

FIG. 5 is a diagrammatic top view of one force measurement assembly usedin the force measurement system with exemplary coordinate axessuperimposed thereon, according to an embodiment of the invention,wherein the force measurement assembly is in the form of a dual forceplate;

FIG. 6 is a diagrammatic perspective view of another force measurementassembly used in the force measurement system, according to anembodiment of the invention, wherein the force measurement assembly isin the form of a single force plate;

FIG. 7 is a diagrammatic top view of another force measurement assemblyused in the force measurement system with exemplary coordinate axessuperimposed thereon, according to an embodiment of the invention,wherein the force measurement assembly is in the form of a single forceplate;

FIG. 8 is a diagrammatic top view of the base assembly and the immersivesubject visual display device of the force measurement system accordingto an embodiment of the invention;

FIG. 9 is a diagrammatic rear view of the base assembly and theimmersive subject visual display device of the force measurement systemaccording to an embodiment of the invention;

FIG. 10 is a diagrammatic side view of the base assembly and theimmersive subject visual display device of the force measurement systemaccording to an embodiment of the invention;

FIG. 11 is a block diagram of constituent components of the forcemeasurement system having a displaceable force measurement assembly,according to an embodiment of the invention;

FIG. 12 is a block diagram illustrating data manipulation operations andmotion control operations carried out by the force measurement system,according to an embodiment of the invention;

FIG. 13 is a single-line diagram of the base assembly electrical powersystem, according to an embodiment of the invention;

FIG. 14 is a first example of a virtual reality scene displayed on thesubject visual display device of the force measurement system, accordingto an embodiment of the invention;

FIG. 15 is a second example of a virtual reality scene displayed on thesubject visual display device of the force measurement system, accordingto an embodiment of the invention;

FIG. 16 is a first variation of an interactive game displayed on thesubject visual display device of the force measurement system, accordingto an embodiment of the invention;

FIG. 17 is a second variation of an interactive game displayed on thesubject visual display device of the force measurement system, accordingto an embodiment of the invention, wherein a game element is in a firstposition;

FIG. 18 is a second variation of an interactive game displayed on thesubject visual display device of the force measurement system, accordingto an embodiment of the invention, wherein the game element is in asecond position;

FIG. 19 is a second variation of an interactive game displayed on thesubject visual display device of the force measurement system, accordingto an embodiment of the invention, wherein the game element is in athird position;

FIG. 20 is a second variation of an interactive game displayed on thesubject visual display device of the force measurement system, accordingto an embodiment of the invention, wherein the game element is in afourth position;

FIG. 21 is a second variation of an interactive game displayed on thesubject visual display device of the force measurement system, accordingto an embodiment of the invention, wherein the game element is in afifth position;

FIG. 22 is a first variation of a training screen image displayed on thesubject visual display device of the force measurement system, accordingto an embodiment of the invention;

FIG. 23 is a second variation of a training screen image displayed onthe subject visual display device of the force measurement system,according to an embodiment of the invention;

FIG. 24 is a third variation of a training screen image displayed on thesubject visual display device of the force measurement system, accordingto an embodiment of the invention;

FIG. 25 is a third variation of an interactive game displayed on thesubject visual display device of the force measurement system, accordingto an embodiment of the invention, wherein the interactive game isprovided with one or more targets and a game element is in a firstposition;

FIG. 26 is a third variation of an interactive game displayed on thesubject visual display device of the force measurement system, accordingto an embodiment of the invention, wherein the interactive game isprovided with one or more targets and the game element is in a secondposition;

FIG. 27 is another example of an interactive game displayed on thesubject visual display device of the force measurement system, accordingto an embodiment of the invention, wherein the interactive game is inthe form of an interactive skiing game;

FIG. 28 is a diagrammatic top view of the base assembly and theimmersive subject visual display device of the force measurement systemaccording to an alternative embodiment of the invention, wherein aprojector with a fisheye lens is disposed in the front of the visualdisplay device and behind the subject;

FIG. 29 is a diagrammatic side view of the base assembly and theimmersive subject visual display device of the force measurement systemaccording to an alternative embodiment of the invention, wherein theprojector with the fisheye lens is disposed in the front of the visualdisplay device and behind the subject;

FIG. 30 is a diagrammatic top view of the base assembly and theimmersive subject visual display device of the force measurement systemaccording to yet another alternative embodiment of the invention,wherein two projectors with respective fisheye lens are disposed in thefront of the visual display device and behind the subject;

FIG. 31 is a diagrammatic side view of the base assembly and theimmersive subject visual display device of the force measurement systemaccording to yet another alternative embodiment of the invention,wherein the two projectors with respective fisheye lens are disposed inthe front of the visual display device and behind the subject;

FIG. 32 is a diagrammatic top view of a force and motion measurementsystem having a motion acquisition/capture system, according to anembodiment of the invention, wherein the motion acquisition/capturesystem is illustrated with the base assembly, the immersive subjectvisual display device, and a subject having a plurality of markersdisposed thereon;

FIG. 33 is a perspective view of a force and motion measurement systemhaving a motion acquisition/capture system, according to an embodimentof the invention, wherein the motion acquisition/capture system isillustrated with the base assembly, the immersive subject visual displaydevice, and a subject having a plurality of markers disposed thereon;

FIG. 34 is a block diagram illustrating a calculation procedure for thejoint angles, velocities, and accelerations, and a calculation procedurefor the joint forces and moments, both of which are carried out by theforce and motion measurement system according to an embodiment of theinvention;

FIG. 35 is a diagrammatic view of a human foot and its typical bonestructure with certain elements of the free body diagram of FIG. 36superimposed thereon, according to an exemplary embodiment of theinvention;

FIG. 36 is a free body diagram that diagrammatically represents theforces and moments acting on the ankle joint according to an exemplaryembodiment of the invention;

FIG. 37 is a third example of a virtual reality scene displayed on thesubject visual display device of the force measurement system, accordingto an embodiment of the invention;

FIG. 38 is a diagrammatic perspective view of an alternative forcemeasurement system comprising an instrumented treadmill and an enlargedhemispherical projection screen, according to an embodiment of theinvention;

FIG. 39A is a schematic side view of a motion base according to anembodiment of the invention;

FIG. 39B is a schematic front view of a motion base according to anembodiment of the invention;

FIG. 40 is a fourth example of a virtual reality scene displayed on thesubject visual display device of the force measurement system, whereinthe virtual reality scene comprises an avatar, according to anembodiment of the invention;

FIG. 41 is a fifth example of a virtual reality scene displayed on thesubject visual display device of the force measurement system, whereinthe virtual reality scene comprises another avatar, according to anembodiment of the invention;

FIG. 42 is a top view of the base assembly illustrated in FIGS. 2 and 3,according to an embodiment of the invention;

FIG. 43 is a longitudinal section cut through the base assemblyillustrated in FIG. 42, wherein the section is cut along the cuttingplane line A-A in FIG. 42, according to an embodiment of the invention;

FIG. 44 is a perspective view of the base assembly and the immersivesubject visual display device of the force measurement system accordingto another alternative embodiment of the invention, wherein a projectorwith an angled fisheye lens is disposed on the top of the visual displaydevice;

FIG. 45 is a diagrammatic perspective view of another alternative forcemeasurement system comprising an instrumented treadmill and an enlargedhemispherical projection screen wherein two projectors with respectivefisheye lens are disposed in the front of the visual display device,according to an embodiment of the invention;

FIG. 46 is a perspective view of yet another alternative forcemeasurement system comprising a displaceable visual surround device, abase assembly, and displaceable force measurement assembly, according toan embodiment of the invention;

FIG. 47 is a first variation of a screen image comprising a plurality ofconcentric bands displayed on the subject visual display device of theforce measurement system, according to an embodiment of the invention,wherein the plurality of concentric bands are generally circular inshape;

FIG. 48 is a second variation of a screen image comprising a pluralityof generally concentric bands displayed on the subject visual displaydevice of the force measurement system, according to an embodiment ofthe invention, wherein the plurality of concentric bands are generallyelliptical or oval in shape;

FIG. 49 is a perspective view of a force and motion measurement systemhaving a motion detection system, according to an embodiment of theinvention, wherein the motion detection system comprises a plurality ofinertial measurement units (IMUs) for detecting the motion of thesubject;

FIG. 50 is a perspective view of a subject interacting with a virtualreality scene displayed on the subject visual display device of theforce measurement system, wherein the subject is outfitted with an eyemovement tracking device having a field-of-view camera and an inertialmeasurement unit attached thereto;

FIG. 51A is a first diagrammatic view of a subject wearing augmentedreality glasses and disposed on a force measurement assembly, whereinthe subject is disposed in an upright position on the force measurementassembly, and the image of the scenery viewed by the subject through theaugmented reality glasses generally matches the actual view of thescenery captured by the camera(s) of the augmented reality glasses;

FIG. 51B is a second diagrammatic view of a subject wearing augmentedreality glasses and disposed on a force measurement assembly, whereinthe subject is in a rearwardly disposed sway angle position on the forcemeasurement assembly, and the image of the scenery viewed by the subjectthrough the augmented reality glasses has been modified so that it doesnot match that the actual view of the scenery captured by the camera(s)of the augmented reality glasses;

FIG. 51C is a third diagrammatic view of a subject wearing augmentedreality glasses and disposed on a force measurement assembly, whereinthe subject is in a forwardly disposed sway angle position on the forcemeasurement assembly, and the image of the scenery viewed by the subjectthrough the augmented reality glasses has been modified so that it doesnot match that the actual view of the scenery captured by the camera(s)of the augmented reality glasses;

FIG. 52 is a perspective view of a subject disposed on a static forcemeasurement assembly and positioned within an immersive subject visualdisplay device, according to yet another alternative embodiment of theinvention;

FIG. 53 is a perspective view of a subject wearing a head-mounted visualdisplay device disposed on a displaceable force measurement assembly,according to still another alternative embodiment of the invention;

FIG. 54 is a perspective view of the base assembly and the immersivesubject visual display device of the force measurement system accordingto yet another alternative embodiment of the invention, wherein thesystem is further provided with a subject harness connected to a forcesensor;

FIG. 55 is an enlarged portion of the perspective view depicted in FIG.54, wherein the harness force sensor is illustrated together with theupper and lower harness connectors;

FIG. 56 is a graph illustrating a vertical force curve generated duringthe performance of a test trial where a subject is pulling on theharness while standing still, according to an embodiment of theinvention;

FIG. 57 is a graph illustrating a vertical force curve generated duringthe performance of a test trial where a subject steps off the forcemeasurement assembly with one foot, and places his or her foot back ontothe force measurement assembly, according to another embodiment of theinvention;

FIG. 58 is a graph illustrating a vertical force curve generated duringthe performance of a test trial where a subject steps off the forcemeasurement assembly with both feet, and does not return to the forcemeasurement assembly, according to another embodiment of the invention;

FIG. 59 is an example of a screen image displayed on the visual displaydevice of the force measurement system, wherein a virtual representationof the subject is depicted using an ankle balance strategy, according toan embodiment of the invention; and

FIG. 60 is an example of a screen image displayed on the visual displaydevice of the force measurement system, wherein a virtual representationof the subject is depicted using a combination hip and ankle balancestrategy, according to an embodiment of the invention.

FIG. 61 is a perspective view of a subject disposed on a displaceableforce measurement assembly while wearing a head-mounted visual displaydevice that creates a virtual screen surround around a flat visualdisplay device, according to yet another alternative embodiment of theinvention;

FIG. 62 is a perspective view of a subject disposed on a displaceableforce measurement assembly while wearing a head-mounted visual displaydevice that creates a virtual visual display device with a virtualscreen surround, according to still another alternative embodiment ofthe invention;

FIG. 63 is a schematic diagram of a first illustrative embodiment ofbiomechanical analysis system that utilizes a displaceable forcemeasurement assembly; and

FIG. 64 is a schematic diagram of a second illustrative embodiment ofbiomechanical analysis system that utilizes a displaceable forcemeasurement assembly.

Throughout the figures, the same parts are always denoted using the samereference characters so that, as a general rule, they will only bedescribed once.

DETAILED DESCRIPTION OF EMBODIMENTS OF THE INVENTION

An exemplary embodiment of the measurement and testing system is seengenerally at 100 in FIG. 1. In the illustrative embodiment, the forcemeasurement system 100 generally comprises a force measurement assembly102 that is operatively coupled to a data acquisition/data processingdevice 104 (i.e., a data acquisition and processing device or computingdevice that is capable of collecting, storing, and processing data),which in turn, is operatively coupled to a subject visual display device107 and an operator visual display device 130. As illustrated in FIG. 1,the force measurement assembly 102 is configured to receive a subject108 thereon, and is capable of measuring the forces and/or momentsapplied to its substantially planar measurement surfaces 114, 116 by thesubject 108.

As shown in FIG. 1, the data acquisition/data processing device 104includes a plurality of user input devices 132, 134 connected thereto.Preferably, the user input devices 132, 134 comprise a keyboard 132 anda mouse 134. In addition, the operator visual display device 130 mayalso serve as a user input device if it is provided with touch screencapabilities. While a desktop-type computing system is depicted in FIG.1, one of ordinary of skill in the art will appreciate that another typeof data acquisition/data processing device 104 can be substituted forthe desktop computing system such as, but not limited to, a laptop or apalmtop computing device (i.e., a PDA). In addition, rather thanproviding a data acquisition/data processing device 104, it is to beunderstood that only a data acquisition device could be provided withoutdeparting from the spirit and the scope of the invention.

Referring again to FIG. 1, it can be seen that the force measurementassembly 102 of the illustrated embodiment is in the form of adisplaceable, dual force plate assembly. The displaceable, dual forceplate assembly includes a first plate component 110, a second platecomponent 112, at least one force measurement device (e.g., a forcetransducer) associated with the first plate component 110, and at leastone force measurement device (e.g., a force transducer) associated withthe second plate component 112. In the illustrated embodiment, a subject108 stands in an upright position on the force measurement assembly 102and each foot of the subject 108 is placed on the top surfaces 114, 116of a respective plate component 110, 112 (i.e., one foot on the topsurface 114 of the first plate component 110 and the other foot on thetop surface 116 of the second plate component 112). The at least oneforce transducer associated with the first plate component 110 isconfigured to sense one or more measured quantities and output one ormore first signals that are representative of forces and/or momentsbeing applied to its measurement surface 114 by the left foot/leg 108 aof the subject 108, whereas the at least one force transducer associatedwith the second plate component 112 is configured to sense one or moremeasured quantities and output one or more second signals that arerepresentative of forces and/or moments being applied to its measurementsurface 116 by the right foot/leg 108 b of subject 108. In one or moreembodiments, when the subject is displaced on the force measurementassembly 102, the subject 108 generally does not move relative to thedisplaceable force measurement assembly 102 (i.e., the subject 108 andthe force measurement assembly 102 generally move together insynchrony). Also, in one or more embodiments, the top surfaces 114, 116of the respective plate components 110, 112 are not rotated underneaththe feet of the subject 108, but rather remain stationary relative tothe feet of the subject 108 (i.e., the top surfaces 114, 116 aredisplaced in generally the same manner as the feet of the subject).

In one non-limiting, exemplary embodiment, the force plate assembly 102has a load capacity of up to approximately 500 lbs. (up to approximately2,224 N) or up to 500 lbs. (up to 2,224 N). Advantageously, this highload capacity enables the force plate assembly 102 to be used withalmost any subject requiring testing on the force plate assembly 102.Also, in one non-limiting, exemplary embodiment, the force plateassembly 102 has a footprint of approximately eighteen (18) inches bytwenty (20) inches. However, one of ordinary skill in the art willrealize that other suitable dimensions for the force plate assembly 102may also be used.

Now, with reference to FIG. 2, it can be seen that the displaceableforce measurement assembly 102 is movably coupled to a base assembly106. The base assembly 106 generally comprises a substantially planarcenter portion 106 b with two spaced-apart side enclosures 106 a, 106 cthat are disposed on opposed sides of the center portion 106 b. As shownin FIG. 2, the displaceable force measurement assembly 102 isrecessed-mounted into the top surface of the center portion 106 b of thebase assembly 106 (i.e., it is recess-mounted into the top surface ofthe translatable sled assembly 156 which is part of the center portion106 b of the base assembly 106) so that its upper surface liessubstantially flush with the adjacent stationary top surfaces 122 a, 122b of the center portion 106 b of the base assembly 106. The uppersurface of the displaceable force measurement assembly 102 also liessubstantially flush with the top surface of the translatable sledassembly 156. Moreover, in the illustrated embodiment, it can be seenthat the base assembly 106 further includes a pair of mounting brackets124 disposed on the outward-facing side surfaces of each side enclosure106 a, 106 c. Each mounting bracket 124 accommodates a respectivesupport rail 128. The support rails 128 can be used for various purposesrelated to the force measurement system 100. For example, the supportrails 128 can be used for supporting a safety harness system, which isworn by the subject during testing so as to prevent injury.

Referring again to FIG. 2, each side enclosure 106 a, 106 c houses aplurality of electronic components that generate a significant amount ofwaste heat that requires venting. Because the bottom of each sideenclosure 106 a, 106 c is substantially open, the waste heat is ventedthrough the bottom thereof. In FIG. 2, it can be seen that the sideenclosure 106 a comprises an emergency stop switch 138 (E-stop) providedin the rear, diagonal panel thereof. In one embodiment, the emergencystop switch 138 is in the form of a red pushbutton that can be easilypressed by a user of the force measurement system 100 in order toquasi-instantaneously stop the displacement of the force measurementassembly 102. As such, the emergency stop switch 138 is a safetymechanism that protects a subject disposed on the displaceable forcemeasurement assembly 102 from potential injury.

Next, turning to FIG. 3, the drive components of the base assembly 106will be described in detail. Initially, the actuator system forproducing the translation of the force measurement assembly 102 will beexplained. In FIG. 3, the front top cover of the center portion 106 b ofthe base assembly 106 has been removed to reveal the translation drivecomponents. As shown in this figure, the force measurement assembly 102is rotatably mounted to a translatable sled assembly 156. Thetranslatable sled assembly 156 is displaced forward and backward (i.e.,in directions generally parallel to the sagittal plane SP of the subject(see e.g., FIG. 1) disposed on the force measurement assembly 102) bymeans of a first actuator assembly 158. That is, the first actuatorassembly 158 moves the translatable sled assembly 156 backwards andforwards, without any substantial rotation or angular displacement(i.e., the first actuator assembly 158 produces generally puretranslational movement). In the illustrated embodiment, the firstactuator assembly 158 is in the form of ball screw actuator, andincludes an electric motor that drives a rotatable screw shaft which, inturn, is threadingly coupled to a nut fixedly secured to thetranslatable sled assembly 156. As such, when the screw shaft of thefirst actuator assembly 158 is rotated by the electric motor, thetranslatable sled assembly is displaced forward and backward along asubstantially linear path. The electric motor of the first actuatorassembly 158 is operatively coupled to a gear box (e.g., a 4:1 gear box)which, in turn, drives the rotatable screw shaft. Advantageously,because the nut of the ball screw actuator runs on ball bearings,friction is minimized and the actuator assembly 158 is highly efficient.However, an undesirable consequence of the highly efficient ball screwactuator design is its back-driveability. This poses a potential safetyhazard to a subject disposed on the displaceable force measurementassembly 102 because the force plate could inadvertently move when asubject's weight is applied thereto. In order to prevent the forcemeasurement assembly 102 from inadvertently being translated, the firstactuator assembly 158 is additionally provided with a brake assemblydisposed adjacent to the electric motor thereof. The brake assembly ofthe first actuator assembly 158 prevents any unintentional translationof the force measurement assembly 102.

In FIG. 42, a top view of the base assembly 106 is illustrated, while inFIG. 43, a longitudinal cross-sectional view of the base assembly 106 isillustrated. As shown in FIGS. 42 and 43, the force measurement assembly102 is mounted on a rotatable carriage assembly 157 (i.e., a swivelframe 157). The rotatable carriage assembly 157 is mounted to, androtates relative to, the translatable sled assembly 156 (i.e., thetranslatable frame 156). The rotatable carriage assembly 157 is rotatedby a second actuator assembly 160 (see FIG. 3) about a rotational shaft163 (see FIG. 43—the rotatable carriage assembly 157 is provided withdiagonal hatching thereon). As indicated by the curved arrows 159 inFIG. 43, the rotatable carriage assembly 157 is capable of eitherclockwise or counter-clockwise rotation about the transverse rotationalaxis TA in FIG. 3 (i.e., generally single degree-of-freedom rotationabout the transverse axis TA). In contrast, as indicated by the straightarrows 161 in FIGS. 42 and 43, the translatable sled assembly 156 iscapable of forward and backward translational movement by virtue ofbeing linearly displaced by first actuator assembly 158. In FIGS. 42 and43, a rearwardly displaced position 156 a of the translatable sledassembly 156 is indicated using center lines, while a forwardlydisplaced position 156 b of the translatable sled assembly 156 isindicated using dashed lines with small dashes.

Again, referring to FIG. 3, the actuator system for producing therotation of the force measurement assembly 102 will now be described. InFIG. 3, the top cover of the side enclosure 106 c of the base assembly106 has been removed to reveal the rotational drive components. Theforce measurement assembly 102 is rotated within the translatable sledassembly 156 by the second actuator assembly 160. Like the firstactuator assembly 158, the second actuator assembly 160 is also in theform of ball screw actuator, and includes an electric motor with a gearbox (e.g., a 4:1 gear box) that drives a rotatable screw shaft which, inturn, is threadingly coupled to a nut that runs on ball bearings.Although, unlike the first actuator assembly 158, the second actuatorassembly 160 further includes a swing arm which is operatively coupledto the nut of the ball screw actuator. When the nut undergoesdisplacement along the screw shaft, the swing arm, which is attached tothe rotatable carriage assembly 157 with the force measurement assembly102, is rotated. As such, when the swing arm is rotated, the rotatablecarriage assembly 157 with the force measurement assembly 102 is alsorotated about a transverse rotational axis TA (see FIG. 3). That is, theforce measurement assembly 102 undergoes generally singledegree-of-freedom rotation about the transverse rotational axis TA. Inone embodiment, the imaginary transverse rotational axis TAapproximately passes through the center of the ankle joints of thesubject 108 when he or she is disposed on the force measurement assembly102. Because the second actuator assembly 160 is also in the form of ahighly efficient ball screw actuator, it includes a brake assemblydisposed adjacent to the electric motor to prevent it from beingback-driven, similar to that of the first actuator assembly 158. Thebrake assembly of the second actuator assembly 160 prevents the forcemeasurement assembly 102 from being inadvertently rotated so as toprotect a subject disposed thereon from its inadvertent movement. Whenthe translatable sled assembly 156 is translated by the first actuatorassembly 158, the second actuator assembly 160 is translated with thesled assembly 156 and the force plate. In particular, when thetranslatable sled assembly 156 is translated backwards and forwards bythe first actuator assembly 158, the second actuator assembly 160 isdisplaced along a rail or rod of the base assembly 106.

In a preferred embodiment of the invention, both the first actuatorassembly 158 and the second actuator assembly 160 are provided with two(2) electrical cables operatively coupled thereto. The first cableconnected to each actuator assembly 158, 160 is a power cable for theelectric motor and brake of each actuator, while the second cabletransmits positional information from the respective actuator encoderthat is utilized in the feedback control of each actuator assembly 158,160.

Referring back to FIG. 1, it can be seen that the base assembly 106 isoperatively coupled to the data acquisition/data processing device 104by virtue of an electrical cable 118. The electrical cable 118 is usedfor transmitting data between the programmable logic controller (PLC) ofthe base assembly 106 and the data acquisition/data processing device104 (i.e., the operator computing device 104). Various types of datatransmission cables can be used for cable 118. For example, the cable118 can be a Universal Serial Bus (USB) cable or an Ethernet cable.Preferably, the electrical cable 118 contains a plurality of electricalwires bundled together that are utilized for transmitting data. However,it is to be understood that the base assembly 106 can be operativelycoupled to the data acquisition/data processing device 104 using othersignal transmission means, such as a wireless data transmission system.

In the illustrated embodiment, the at least one force transducerassociated with the first and second plate components 110, 112 comprisesfour (4) pylon-type force transducers 154 (or pylon-type load cells)that are disposed underneath, and near each of the four corners (4) ofthe first plate component 110 and the second plate component 112 (seeFIG. 4). Each of the eight (8) illustrated pylon-type force transducershas a plurality of strain gages adhered to the outer periphery of acylindrically-shaped force transducer sensing element for detecting themechanical strain of the force transducer sensing element impartedthereon by the force(s) applied to the surfaces of the force measurementassembly 102. As shown in FIG. 4, a respective base plate 162 can beprovided underneath the transducers 154 of each plate component 110, 112for facilitating the mounting of the force plate assembly to therotatable carriage assembly 157 of the translatable sled assembly 156 ofthe base assembly 106. Alternatively, a plurality of structural framemembers (e.g., formed from steel) could be used in lieu of the baseplates 162 for attaching the dual force plate assembly to the rotatablecarriage assembly 157 of the translatable sled assembly 156 of the baseassembly 106.

In an alternative embodiment, rather than using four (4) pylon-typeforce transducers 154 on each plate component 110, 112, forcetransducers in the form of transducer beams could be provided under eachplate component 110, 112. In this alternative embodiment, the firstplate component 110 could comprise two transducer beams that aredisposed underneath, and on generally opposite sides of the first platecomponent 110. Similarly, in this embodiment, the second plate component112 could comprise two transducer beams that are disposed underneath,and on generally opposite sides of the second plate component 112.Similar to the pylon-type force transducers 154, the force transducerbeams could have a plurality of strain gages attached to one or moresurfaces thereof for sensing the mechanical strain imparted on the beamby the force(s) applied to the surfaces of the force measurementassembly 102.

Rather, than using four (4) force transducer pylons under each plate, ortwo spaced apart force transducer beams under each plate, it is to beunderstood that the force measurement assembly 102 can also utilize theforce transducer technology described in U.S. Pat. No. 8,544,347, theentire disclosure of which is incorporated herein by reference.

In other embodiments of the invention, rather than using a forcemeasurement assembly 102 having first and second plate components 110,112, it is to be understood that a force measurement assembly 102′ inthe form of a single force plate may be employed (see FIG. 6). Unlikethe dual force plate assembly illustrated in FIGS. 1 and 4, the singleforce plate comprises a single measurement surface on which both of asubject's feet are placed during testing. Although, similar to themeasurement assembly 102, the illustrated single force plate 102′comprises four (4) pylon-type force transducers 154 (or pylon-type loadcells) that are disposed underneath, and near each of the four corners(4) thereof for sensing the load applied to the surface of the forcemeasurement assembly 102′. Also, referring to FIG. 6, it can be seenthat the single force plate 102′ may comprise a single base plate 162′disposed beneath the four (4) pylon-type force transducers 154.

Referring to FIGS. 2 and 3, the base assembly 106 is preferably providedwith a plurality of support feet 126 disposed thereunder. Preferably,each of the four (4) corners of the base assembly 106 is provided with asupport foot 126. In one embodiment, each support foot 126 is attachedto a bottom surface of base assembly 106. In one preferred embodiment,at least one of the support feet 126 is adjustable so as to facilitatethe leveling of the base assembly 106 on an uneven floor surface (e.g.,see FIG. 3, the support foot can be provided with a threaded shaft 129that permits the height thereof to be adjusted). For example, referringto FIG. 2, the right corner of the base assembly 106 may be providedwith a removable cover plate 127 for gaining access to an adjustablesupport foot 126 with threaded shaft 129.

In one exemplary embodiment, with reference to FIG. 2, the base assembly106 has a length L_(B) of approximately five feet (5′-0″), a width W_(B)of approximately five feet (5′-0″), and a step height H_(B) ofapproximately four (4) inches. In other words, the base assembly has anapproximately 5′-0″ by 5′-0″ footprint with step height of approximatelyfour (4) inches. In other exemplary embodiments, the base assembly 106has a width W_(B) of slightly less than five feet (5′-0″), for example,a width W_(B) lying in the range between approximately fifty-two (52)inches and approximately fifty-nine (59) inches (or between fifty-two(52) inches and fifty-nine (59) inches). Also, in other exemplaryembodiments, the base assembly 106 has a step height lying in the rangebetween approximately four (4) inches and approximately four andone-half (4½) inches (or between four (4) inches and four and one-half(4½) inches). Advantageously, the design of the base assembly 106 issuch that its step height is minimized. For example, the placement ofthe second actuator assembly 160 above the top surface of the baseassembly 106 facilitates a reduction in the step height of the baseassembly 106. It is highly desirable for the base assembly 106 to haveas low a profile as possible. A reduced step height especially makes iteasier for subjects having balance disorders to step on and off the baseassembly 106. This reduced step height is particularly advantageous forelderly subjects or patients being tested on the force measurementsystem 100 because it is typically more difficult for elderly subjectsto step up and down from elevated surfaces.

Now, with reference to FIGS. 8-10, the subject visual display device 107of the force measurement system 100 will be described in more detail. Inthe illustrated embodiment, the subject visual display device 107generally comprises a projector 164, a generally spherical mirror 166(i.e., a convexly curved mirror that has the shape of a piece cut out ofa spherical surface), and a generally hemispherical concave projectionscreen 168 with a variable radius (i.e., the radius of the hemisphericalprojection screen 168 becomes increasingly larger from its center to itsperiphery—see radii R1, R2, and R3 in FIG. 10). As shown in FIGS. 8-10,the hemispherical projection screen 168 may be provided with aperipheral flange 169 therearound. The lens of the projector 164projects an image onto the generally spherical mirror 166 which, inturn, projects the image onto the generally hemispherical projectionscreen 168 (see FIG. 10). As shown in FIGS. 8 and 10, the top of thegenerally hemispherical projection screen 168 is provided with asemi-circular cutout 180 for accommodating the projector light beam 165in the illustrative embodiment. Advantageously, the generallyhemispherical projection screen 168 is a continuous curved surface thatdoes not contain any lines or points resulting from the intersection ofadjoining planar or curved surfaces. Thus, the projection screen 168 iscapable of creating a completely immersive visual environment for asubject being tested on the force measurement assembly 102 because thesubject is unable to focus on any particular reference point or line onthe screen 168. As such, the subject becomes completely immersed in thevirtual reality scene(s) being projected on the generally hemisphericalprojection screen 168, and thus, his or her visual perception can beeffectively altered during a test being performed using the forcemeasurement system 100 (e.g., a balance test). In order to permit asubject to be substantially circumscribed by the generally hemisphericalprojection screen 168 on three sides, the bottom of the screen 168 isprovided with a semi-circular cutout 178 in the illustrative embodiment.While the generally hemispherical projection screen 168 thoroughlyimmerses the subject 108 in the virtual reality scene(s), itadvantageously does not totally enclose the subject 108. Totallyenclosing the subject 108 could cause him or her to become extremelyclaustrophobic. Also, the clinician would be unable to observe thesubject or patient in a totally enclosed environment. As such, theillustrated embodiment of the force measurement system 100 does notutilize a totally enclosed environment, such as a closed, rotatingshell, etc. Also, as shown in FIGS. 1-3 and 8-10, the subject visualdisplay device 107 is not attached to the subject 108, and it is spacedapart from the force measurement assembly 102 disposed in the baseassembly 106.

In one embodiment of the invention, the generally hemisphericalprojection screen 168 is formed from a suitable material (e.g., anacrylic, fiberglass, fabric, aluminum, etc.) having a matte gray color.A matte gray color is preferable to a white color because it minimizesthe unwanted reflections that can result from the use of a projectionscreen having a concave shape. Also, in an exemplary embodiment, theprojection screen 168 has a diameter (i.e., width W_(S)) ofapproximately 69 inches and a depth D_(S) of approximately 40 inches(see FIGS. 8 and 9). In other exemplary embodiments, the projectionscreen 168 has a width W_(S) lying in the range between approximatelysixty-eight (68) inches and approximately ninety-two (92) inches (orbetween sixty-eight (68) inches and ninety-two (92) inches). Forexample, including the flange 169, the projection screen 168 could havea width W_(S) of approximately seventy-three (73) inches. In someembodiments, the target distance between the subject and the frontsurface of the projection screen 168 can lie within the range betweenapproximately 25 inches and approximately 40 inches (or between 25inches and 40 inches). Although, those of ordinary skill in the art willreadily appreciate that other suitable dimensions and circumscribinggeometries may be utilized for the projection screen 168, provided thatthe selected dimensions and circumscribing geometries for the screen 168are capable of creating an immersive environment for a subject disposedon the force measurement assembly 102 (i.e., the screen 168 of thesubject visual display device engages enough of the subject's peripheralvision such that the subject becomes, and remains immersed in thevirtual reality scenario). In one or more embodiments, the projectionscreen 168 fully encompasses the peripheral vision of the subject 108(e.g., by the coronal plane CP of the subject being approximatelyaligned with the flange 169 of the projection screen 168 or by thecoronal plane CP being disposed inwardly from the flange 169 within thehemispherical confines of the screen 168). In other words, the outputscreen 168 of the at least one visual display 107 at least partiallycircumscribes three sides of a subject 108 (e.g., see FIG. 1). As shownin FIGS. 8-10, a top cover 171 is preferably provided over the projector164, the mirror 166, and the cutout 180 in the output screen 168 so asto protect these components, and to give the visual display device 107 amore finished appearance.

In a preferred embodiment, the data acquisition/data processing device104 is configured to convert a two-dimensional (2-D) image, which isconfigured for display on a conventional two-dimensional screen, into athree-dimensional (3-D) image that is capable of being displayed on thehemispherical output screen 168 without excessive distortion. That is,the data acquisition/data processing device 104 executes a softwareprogram that utilizes a projection mapping algorithm to “warp” a flat2-D rendered projection screen image into a distorted 3-D projectionimage that approximately matches the curvature of the final projectionsurface (i.e., the curvature of the hemispherical output screen 168),which takes into account both the distortion of the lens of theprojector 164 and any optical surfaces that are used to facilitate theprojection (e.g., generally spherical mirror 166). In particular, theprojection mapping algorithm utilizes a plurality of virtual cameras andprojection surfaces (which are modeled based upon the actual projectionsurfaces) in order to transform the two-dimensional (2-D) images intothe requisite three-dimensional (3-D) images. Thus, the projector 164lens information, the spherical mirror 166 dimensional data, and thehemispherical projection screen 168 dimensional data are entered asinputs into the projection mapping algorithm software. When a humansubject is properly positioned in the confines of the hemisphericaloutput screen 168, he or she will see a representation of the virtualreality scene wrapping around them instead of only seeing a smallviewing window in front of him or her. Advantageously, using a softwarepackage comprising a projection mapping algorithm enables the system 100to use previously created 3-D modeled virtual worlds and objects withoutdirectly modifying them. Rather, the projection mapping algorithmemployed by the software package merely changes the manner in whichthese 3-D modeled virtual worlds and objects are projected into thesubject's viewing area.

Those of ordinary skill in the art will also appreciate that the subjectvisual display device 107 may utilize other suitable projection means.For example, rather using an overhead-type projector 164 as illustratedin FIGS. 8-10, a direct or rear projection system can be utilized forprojecting the image onto the screen 168, provided that the directprojection system does not interfere with the subject's visibility ofthe target image. In such a rear or direct projection arrangement, thegenerally spherical mirror 166 would not be required. With reference toFIGS. 28 and 29, in one exemplary embodiment, a single projector 164′with a fisheye-type lens and no mirror is utilized in the subject visualdisplay system to project an image onto the screen 168 (e.g., theprojector 164′ is disposed behind the subject 108). As illustrated inthese figures, the projector 164′ with the fisheye-type lens projects alight beam 165′ through the cutout 180 in the top of the generallyhemispherical projection screen 168. In another exemplary embodiment,two projectors 164′, each having a respective fisheye-type lens, areused to project an image onto the screen 168 (see FIGS. 30 and 31—theprojectors 164′ are disposed behind the subject 108). As depicted FIGS.30 and 31, the projectors 164′ with the fisheye-type lens projectintersecting light beams 165′ through the cutout 180 in the top of thegenerally hemispherical projection screen 168. Advantageously, the useof two projectors 164′ with fisheye-type lens, rather than just a singleprojector 164′ with a fisheye lens, has the added benefit of removingshadows that are cast on the output screen 168 by the subject 108disposed on the force measurement assembly 102.

Another alternative embodiment of the projector arrangement isillustrated in FIG. 44. As shown in this figure, a projector 164″ havinga fisheye lens 182 is mounted on the top of the hemispherical projectionscreen 168. In FIG. 44, it can be seen that the fisheye lens 182 isconnected to the body of the projector 164″ by an elbow fitting 184. Inother words, the fisheye lens 182 is disposed at a non-zero, angledorientation relative to a body of the projector 164″. In the illustratedembodiment, the non-zero, angled orientation at which the fisheye lens182 is disposed relative to the body of the projector 164″ isapproximately 90 degrees. The elbow fitting 184 comprises a one-waymirror disposed therein for changing the direction of the light beamemanating from the projector 164″. As illustrated in FIG. 44, thefisheye lens 182 is disposed at approximately the apex of thehemispherical projection screen 168, and it extends down through thecutout 180′ at the top of the screen 168. Because a fisheye lens 182 isutilized in the arrangement of FIG. 44, the generally spherical mirror166 is not required, similar to that which was described above for theembodiment of FIGS. 28 and 29.

Referring again to FIG. 44, it can be seen that the generallyhemispherical projection screen 168 can be supported from a floorsurface using a screen support structure 186, which is an alternativedesign to that which is illustrated in FIGS. 2 and 8-10. As describedabove for the screen support structure 167, the screen support structure186 is used to elevate the projection screen 168 a predetermineddistance above the floor of a room. With continued reference to FIG. 44,it can be seen that the illustrated screen support structure 186comprises a plurality of lower leg members 187 (i.e., four (4) legmembers 187) that support an upper support cage portion 189, which isdisposed around the upper portion of the generally hemisphericalprojection screen 168. In particular, the upper support cage portion 189is securely attached to the peripheral flange 169 of the hemisphericalprojection screen 168 (e.g., by using a plurality of fasteners on eachside of the flange 169). Because the upper support cage portion 189 ismostly attached to the upper portion (e.g., upper half) of the screen168, the screen 168 is generally supported above its center-of-gravity,which advantageously results in a screen mounting arrangement with highstructural stability. As shown in FIG. 44, one pair of the plurality oflower leg members 187 are disposed on each of the opposed lateral sidesof the screen 168. Also, it can be seen that each of the lower legmembers 187 is provided with a height-adjustable foot 188 for adjustingthe height of the screen 168 relative to the floor. Also, as shown inFIG. 44, the projector 164″ is supported on the top of the screen 168 bya projector support frame 190, which is secured directly to the uppersupport cage portion 189 of the screen support structure 186 so as tominimize the transmission of vibrations from the projector 164″ to thehemispherical projection screen 168. Advantageously, the mountingarrangement of the projector 164″ on the projector support frame 190affords adjustability of the projector 164″ in a front-to-backdirection. It is highly desirable for the hemispherical projectionscreen 168 to be maintained in a stationary position essentially freefrom external vibrations so that the subject is completely immersed inthe virtual environment being created within the hemisphericalprojection screen 168. Advantageously, the structural rigidity affordedby the screen support structure 186 of FIG. 44 virtually eliminates thetransmission of vibrations to the projection screen 168, including thosevibrations emanating from the building itself in which the forcemeasurement system 100 is located. In particular, the screen supportstructure 186 is designed to minimize any low frequency vibrations thatare transmitted to the screen 168. In addition, the elimination of thegenerally spherical mirror 166 from the projector arrangement in FIG.44, minimizes the transmission of visible vibrations to the screen imagethat is projected onto the hemispherical projection screen 168 by theprojector 164″.

In one or more embodiments, the base assembly 106 has a width W_(B) (seee.g., FIG. 2) measured in a direction generally parallel to the coronalplane CP of the subject (see e.g., FIG. 1) and a length L_(B) (FIG. 2)measured in a direction generally parallel to the sagittal plane SP ofthe subject (FIG. 1). In these one or more embodiments, a width W_(S) ofthe output screen 168 of the at least one visual display device 107 (seeFIG. 9) is less than approximately 1.5 times the width W_(B) of the baseassembly 106 (or less than 1.5 times the width W_(B) of the baseassembly 106), and a depth D_(S) of the output screen 168 of the atleast one visual display device 107 (see FIG. 8) is less than the lengthL_(B) of the base assembly 106 (FIG. 2). As shown in FIG. 9, in theillustrated embodiment, the width W_(S) of the output screen 168 of theat least one visual display device 107 is greater than the width W_(B)of the base assembly 106. In some embodiments, a width W_(S) of theoutput screen 168 of the at least one visual display device 107 (seeFIG. 9) is greater than approximately 1.3 times the width W_(B) of thebase assembly 106 (or greater than 1.3 times the width W_(B) of the baseassembly 106).

As illustrated in FIGS. 2 and 8-10, the generally hemisphericalprojection screen 168 can be supported from a floor surface using ascreen support structure 167. In other words, the screen supportstructure 167 is used to elevate the projection screen 168 apredetermined distance above the floor of a room. With continuedreference to FIGS. 2 and 8-10, it can be seen that the illustratedscreen support structure 167 comprises a lower generally U-shaped member167 a, an upper generally U-shaped member 167 b, and a plurality ofvertical members 167 c, 167 d, 167 e. As best shown in FIGS. 2, 9, and10, the two vertical members 167 c, 167 d are disposed on opposite sidesof the screen 168, while the third vertical member 167 e is disposedgenerally in the middle of, and generally behind, the screen 168. Thescreen support structure 167 maintains the projection screen 168 in astationary position. As such, the position of the projection screen 168is generally fixed relative to the base assembly 106. In the side viewof FIG. 10, it can be seen that the rearmost curved edge of theprojection screen 168 is generally aligned with the back edge of thebase assembly 106.

Next, referring again to FIG. 1, the operator visual display device 130of the force measurement system 100 will be described in moreparticularity. In the illustrated embodiment, the operator visualdisplay device 130 is in the form of a flat panel monitor. Those ofordinary skill in the art will readily appreciate that various types offlat panel monitors having various types of data transmission cables 140may be used to operatively couple the operator visual display device 130to the data acquisition/data processing device 104. For example, theflat panel monitor employed may utilize a video graphics array (VGA)cable, a digital visual interface (DVI or DVI-D) cable, ahigh-definition multimedia interface (HDMI or Mini-HDMI) cable, or aDisplayPort digital display interface cable to connect to the dataacquisition/data processing device 104. Alternatively, in otherembodiments of the invention, the visual display device 130 can beoperatively coupled to the data acquisition/data processing device 104using wireless data transmission means. Electrical power is supplied tothe visual display device 130 using a separate power cord that connectsto a building wall receptacle.

Also, as shown in FIG. 1, the subject visual display device 107 isoperatively coupled to the data acquisition/data processing device 104by means of a data transmission cable 120. More particularly, theprojector 164 of the subject visual display device 107 is operativelyconnected to the data acquisition/data processing device 104 via thedata transmission cable 120. Like the data transmission cable 140described above for the operator visual display device 130, varioustypes of data transmission cables 120 can be used to operatively connectthe subject visual display device 107 to the data acquisition/dataprocessing device 104 (e.g., the various types described above).

Those of ordinary skill in the art will appreciate that the visualdisplay device 130 can be embodied in various forms. For example, if thevisual display device 130 is in the form of flat screen monitor asillustrated in FIG. 1, it may comprise a liquid crystal display (i.e.,an LCD display), a light-emitting diode display (i.e., an LED display),a plasma display, a projection-type display, or a rear projection-typedisplay. The operator visual display device 130 may also be in the formof a touch pad display. For example, the operator visual display device130 may comprise multi-touch technology which recognizes two or morecontact points simultaneously on the surface of the screen so as toenable users of the device to use two fingers for zooming in/out,rotation, and a two finger tap.

Now, turning to FIG. 11, it can be seen that the illustrated dataacquisition/data processing device 104 (i.e., the operator computingdevice) of the force measurement system 100 includes a microprocessor104 a for processing data, memory 104 b (e.g., random access memory orRAM) for storing data during the processing thereof, and data storagedevice(s) 104 c, such as one or more hard drives, compact disk drives,floppy disk drives, flash drives, or any combination thereof. As shownin FIG. 11, the programmable logic controller (PLC) of the base assembly106, the subject visual display device 107, and the operator visualdisplay device 130 are operatively coupled to the data acquisition/dataprocessing device 104 such that data is capable of being transferredbetween these devices 104, 106, 107, and 130. Also, as illustrated inFIG. 11, a plurality of data input devices 132, 134 such as the keyboard132 and mouse 134 shown in FIG. 1, are operatively coupled to the dataacquisition/data processing device 104 so that a user is able to enterdata into the data acquisition/data processing device 104. In someembodiments, the data acquisition/data processing device 104 can be inthe form of a desktop computer, while in other embodiments, the dataacquisition/data processing device 104 can be embodied as a laptopcomputer.

Advantageously, the programmable logic controller 172 of the baseassembly 106 (see e.g., FIGS. 12 and 13, which is a type of dataprocessing device) provides real-time control of the actuator assemblies158, 160 that displace the force measurement assembly 102 (i.e, forceplate assembly 102). The real-time control provided by the programmablelogic controller 172 ensures that the motion control software regulatingthe displacement of the force plate assembly 102 operates at the designclock rate, thereby providing fail-safe operation for subject safety. Inone embodiment, the programmable logic controller 172 comprises both themotion control software and the input/output management software, whichcontrols the functionality of the input/output (I/O) module of theprogrammable logic controller 172. In one embodiment, the programmablelogic controller 172 utilizes EtherCAT protocol for enhanced speedcapabilities and real-time control.

In one or more embodiments, the input/output (I/O) module of theprogrammable logic controller 172 allows various accessories to be addedto the force measurement system 100. For example, an eye movementtracking system, such as that described by U.S. Pat. Nos. 6,113,237 and6,152,564 could be operatively connected to the input/output (I/O)module of the programmable logic controller 172. As another example, ahead movement tracking system, which is instrumented with one or moreaccelerometers, could be operatively connected to the input/output (I/O)module.

FIG. 12 graphically illustrates the acquisition and processing of theload data and the control of the actuator assemblies 158, 160 carriedout by the exemplary force measurement system 100. Initially, as shownin FIG. 12, a load L is applied to the force measurement assembly 102 bya subject disposed thereon. The load is transmitted from the first andsecond plate components 110, 112 to its respective set of pylon-typeforce transducers or force transducer beams. As described above, in oneembodiment of the invention, each plate component 110, 112 comprisesfour (4) pylon-type force transducers 154 disposed thereunder.Preferably, these pylon-type force transducers 154 are disposed nearrespective corners of each plate component 110, 112. In a preferredembodiment of the invention, each of the pylon-type force transducersincludes a plurality of strain gages wired in one or more Wheatstonebridge configurations, wherein the electrical resistance of each straingage is altered when the associated portion of the associated pylon-typeforce transducer undergoes deformation resulting from the load (i.e.,forces and/or moments) acting on the first and second plate components110, 112. For each plurality of strain gages disposed on the pylon-typeforce transducers, the change in the electrical resistance of the straingages brings about a consequential change in the output voltage of theWheatstone bridge (i.e., a quantity representative of the load beingapplied to the measurement surface). Thus, in one embodiment, the four(4) pylon-type force transducers 154 disposed under each plate component110, 112 output a total of three (3) analog output voltages (signals).In some embodiments, the three (3) analog output voltages from eachplate component 110, 112 are then transmitted to an analog preamplifierboard 170 in the base assembly 106 for preconditioning (i.e., signalsS_(FPO1)-S_(FPO6) in FIG. 12). The preamplifier board is used toincrease the magnitudes of the transducer analog output voltages. Afterwhich, the analog force plate output signals S_(APO1)-S_(APO6) aretransmitted from the analog preamplifier 170 to the programmable logiccontroller (PLC) 172 of the base assembly 106. In the programmable logiccontroller (PLC) 172, analog force plate output signalsS_(APO1)-S_(APO6) are converted into forces, moments, centers ofpressure (COP), and/or a center of gravity (COG) for the subject. Then,the forces, moments, centers of pressure (COP), subject center ofgravity (COG), and/or sway angle for the subject computed by theprogrammable logic controller 172 are transmitted to the dataacquisition/data processing device 104 (operator computing device 104)so that they can be utilized in reports displayed to an operator OP.Also, in yet another embodiment, the preamplifier board 170 additionallycould be used to convert the analog voltage signals into digital voltagesignals (i.e., the preamplifier board 170 could be provided with ananalog-to-digital converter). In this embodiment, digital voltagesignals would be transmitted to the programmable logic controller (PLC)172 rather than analog voltage signals.

When the programmable logic controller 172 receives the voltage signalsS_(ACO1)-S_(ACO6), it initially transforms the signals into outputforces and/or moments by multiplying the voltage signalsS_(ACO1)-S_(ACO6) by a calibration matrix (e.g., F_(Lz), M_(Lx), M_(Ly),F_(Rz), M_(Rx), M_(Ry)). After which, the the center of pressure foreach foot of the subject (i.e., the x and y coordinates of the point ofapplication of the force applied to the measurement surface by eachfoot) are determined by the programmable logic controller 172. Referringto FIG. 5, which depicts a top view of the measurement assembly 102, itcan be seen that the center of pressure coordinates (x_(P) _(L) , y_(P)_(L) ) for the first plate component 110 are determined in accordancewith x and y coordinate axes 142, 144. Similarly, the center of pressurecoordinates (x_(P) _(R) , y_(P) _(R) ) for the second plate component112 are determined in accordance with x and y coordinate axes 146, 148.If the force transducer technology described in U.S. Pat. No. 8,544,347is employed, it is to be understood that the center of pressurecoordinates (x_(P) _(L) , y_(P) _(L) , x_(P) _(R) , x_(P) _(R) ) can becomputed in the particular manner described in that application.

As explained above, rather than using a measurement assembly 102 havingfirst and second plate components 110, 112, a force measurement assembly102′ in the form of a single force plate may be employed (see FIGS. 6and 7, which illustrate a single force plate). As discussedhereinbefore, the single force plate comprises a single measurementsurface on which both of a subject's feet are placed during testing. Assuch, rather than computing two sets of center of pressure coordinates(i.e., one for each foot of the subject), the embodiments employing thesingle force plate compute a single set of overall center of pressurecoordinates (x_(P), y_(P)) in accordance with x and y coordinate axes150, 152.

In one exemplary embodiment, the programmable logic controller 172 inthe base assembly 106 determines the vertical forces F_(Lz), F_(Rz)exerted on the surface of the first and second force plates by the feetof the subject and the center of pressure for each foot of the subject,while in another exemplary embodiment, the output forces of the dataacquisition/data processing device 104 include all three (3) orthogonalcomponents of the resultant forces acting on the two plate components110, 112 (i.e., F_(Lx), F_(Ly), F_(Lz), F_(Rx), F_(Ry), F_(Rz)) and allthree (3) orthogonal components of the moments acting on the two platecomponents 110, 112 (i.e., M_(Lx), M_(Ly), M_(Lz), M_(Rx), M_(Ry),M_(Rz)). In yet other embodiments of the invention, the output forcesand moments of the data acquisition/data processing device 104 can be inthe form of other forces and moments as well.

In the illustrated embodiment, the programmable logic controller 172converts the computed center of pressure (COP) to a center of gravity(COG) for the subject using a Butterworth filter. For example, in oneexemplary, non-limiting embodiment, a second-order Butterworth filterwith a 0.75 Hz cutoff frequency is used. In addition, the programmablelogic controller 172 also computes a sway angle for the subject using acorrected center of gravity (COG′) value, wherein the center of gravity(COG) value is corrected to accommodate for the offset position of thesubject relative to the origin of the coordinate axes (142, 144, 146,148) of the force plate assembly 102. For example, the programmablelogic controller 172 computes the sway angle for the subject in thefollowing manner:

$\begin{matrix}{\theta = {{\sin^{- 1}\left( \frac{{COG}^{\prime}}{0.55h} \right)} - {2.3^{\circ}}}} & (1)\end{matrix}$where:θ: sway angle of the subject;COG′: corrected center of gravity of the subject; andh: height of the center of gravity of the subject.

Now, referring again to the block diagram of FIG. 12, the manner inwhich the motion of the force measurement assembly 102 is controlledwill be explained. Initially, an operator OP inputs one or more motioncommands at the operator computing device 104 (data acquisition/dataprocessing device 104) by utilizing one of the user input devices 132,134. Once, the one or more motion commands are processed by the operatorcomputing device 104, the motion command signals are transmitted to theprogrammable logic controller 172. Then, after further processing by theprogrammable logic controller 172, the motion command signals aretransmitted to the actuator control drive 174. Finally, the actuatorcontrol drive 174 transmits the direct-current (DC) motion commandsignals to the first and second actuator assemblies 158, 160 so that theforce measurement assembly 102, and the subject disposed thereon, can bedisplaced in the desired manner. The actuator control drive 174 controlsthe position, velocity, and torque of each actuator motor.

In order to accurately control the motion of the force measurementassembly 102, a closed-loop feedback control routine may be utilized bythe force measurement system 100. As shown in FIG. 12, the actuatorcontrol drive 174 receives the position, velocity, and torque of eachactuator motor from the encoders provided as part of each actuatorassembly 158, 160. Then, from the actuator control drive 174, theposition, velocity, and torque of each actuator motor is transmitted tothe programmable logic controller 172, wherein the feedback control ofthe first and second actuator assemblies 158, 160 is carried out. Inaddition, as illustrated in FIG. 12, the position, velocity, and torqueof each actuator motor is transmitted from the programmable logiccontroller 172 to the operator computing device 104 so that it iscapable of being used to characterize the movement of the subject on theforce measurement assembly 102 (e.g., the motor positional data and/ortorque can be used to compute the sway of the subject). Also, therotational and translational positional data that is received from firstand second actuator assemblies 158, 160 can be transmitted to theoperator computing device 104.

Next, the electrical single-line diagram of FIG. 13, which schematicallyillustrates the power distribution system for the base assembly 106,will be explained. As shown in this figure, the building power supply iselectrically coupled to an isolation transformer 176 (also refer to FIG.3). In one exemplary embodiment, the isolation transformer 176 is amedical-grade isolation transformer that isolates the electrical systemof the base assembly 106 from the building electrical system. Theisolation transformer 176 greatly minimizes any leakage currents fromthe building electrical system, which could pose a potential safetyhazard to a subject standing on the metallic base assembly 106. Theprimary winding of the isolation transformer 176 is electrically coupledto the building electrical system, whereas the secondary winding ofisolation transformer 176 is electrically coupled to the programmablelogic controller 172 (as schematically illustrated in FIG. 13).

Referring again to FIG. 13, it can be seen that the programmable logiccontroller 172 is electrically coupled to the actuator control drive 174via an emergency stop (E-stop) switch 138. As explained above, in oneembodiment, the emergency stop switch 138 is in the form of a redpushbutton that can be easily pressed by a user of the force measurementsystem 100 (e.g., a subject on the force measurement assembly 102 or anoperator) in order to quasi-instantaneously stop the displacement of theforce measurement assembly 102. Because the emergency stop switch 138 isdesigned to fail open, the emergency stop switch 138 is a fail-safemeans of aborting the operations (e.g., the software operations)performed by the programmable logic controller 172. Thus, even if theprogrammable logic controller 172 fails, the emergency stop switch 138will not fail, thereby cutting the power to the actuator control drive174 so that the force measurement assembly 102 remains stationary (i.e.,the brakes on the actuator assemblies 158, 160 will engage, and thus,prevent any intentional movement thereof). Also, in one embodiment, theemergency stop switch assembly 138 includes a reset button forre-enabling the operation of the actuator control drive 174 after it ishas been shut down by the emergency stop switch.

As shown in FIG. 13, the first and second actuator assemblies 158, 160are powered by the actuator control drive 174. While not explicitlyshown in FIG. 13, the electrical system of the base assembly 106 mayfurther include a power entry module that includes a circuit breaker(e.g., a 20 A circuit breaker) and a filter. Also, the electrical systemof the base assembly 106 may additionally include an electromagneticinterference (EMI) filter that reduces electrical noise so as to meetthe requirements of the Federal Communications Commission (FCC).

Now, specific functionality of the immersive virtual reality environmentof the force measurement system 100 will be described in detail. It isto be understood that the aforedescribed functionality of the immersivevirtual reality environment of the force measurement system 100 can becarried out by the data acquisition/data processing device 104 (i.e.,the operator computing device) utilizing software, hardware, or acombination of both hardware and software. For example, the dataacquisition/data processing device 104 can be specially programmed tocarry out the functionality described hereinafter. In one embodiment ofthe invention, the computer program instructions necessary to carry outthis functionality may be loaded directly onto an internal data storagedevice 104 c of the data acquisition/data processing device 104 (e.g.,on a hard drive thereof) and subsequently executed by the microprocessor104 a of the data acquisition/data processing device 104. Alternatively,these computer program instructions could be stored on a portablecomputer-readable medium (e.g., a flash drive, a floppy disk, a compactdisk, etc.), and then subsequently loaded onto the data acquisition/dataprocessing device 104 such that the instructions can be executedthereby. In one embodiment, these computer program instructions areembodied in the form of a virtual reality software program executed bythe data acquisition/data processing device 104. In other embodiments,these computer program instructions could be embodied in the hardware ofthe data acquisition/data processing device 104, rather than in thesoftware thereof. It is also possible for the computer programinstructions to be embodied in a combination of both the hardware andthe software.

In alternative embodiments of the invention, a force measurementassembly 102 in the form of a static force plate (i.e., the force platesurface is stationary and is not displaced relative to the floor orground) can be used with the immersive virtual reality environmentdescribed herein. Such a static force plate does not have any actuatorsor other devices that translate or rotate the force measurementsurface(s) thereof. For example, as shown in FIG. 52, the static forceplate 102′ is disposed beneath the semi-circular cutout 178 of thegenerally hemispherical projection screen 168 of the visual displaydevice 107. As depicted in FIG. 52, the static force plate 102′ isvertically aligned with the semi-circular cutout 178 in the bottomportion of the generally hemispherical projection screen 168 (i.e., whena subject 108 stands on the static force plate 102′, his or her legspass through the semi-circular cutout 178 in the bottom portion of thegenerally hemispherical projection screen 168 so that he or she is ableto become fully immersed in the simulated environment created by thescenes displayed on the screen 168). As described in detail hereinafter,the data acquisition/data processing device of the force measurementsystem illustrated in FIG. 52 may be programmed to perturb the visualinput of the subject 108 during the performance of a balance test ortraining routine by manipulating the scenes on the output screen 168 ofthe visual display device 107. During the performance of the balancetest or training routine while the subject is disposed on the staticforce plate 102′, the data acquisition/data processing device may befurther programmed to utilize the output forces and/or moments computedfrom the output data of the static force plate 102′ in order to assess aresponse of the subject to the visual stimuli on the generallyhemispherical projection screen 168 of the visual display device 107.For example, to assess the response of the subject 108 during theperformance of the balance test or training routine, the output forcesand/or moments determined using the static force plate 102′ may be usedto determine any of the scores or parameters (i)-(viii) described belowin conjunction with the embodiment illustrated in FIG. 53.

As described above, in one or more embodiments of the invention, one ormore virtual reality scenes are projected on the generally hemisphericalprojection screen 168 of the subject visual display device 107 so thatthe visual perception of a subject can be effectively altered during atest being performed using the force measurement system 100 (e.g., abalance test). In order to illustrate the principles of the invention,the immersive virtual reality environment of the force measurementsystem 100 will be described in conjunction with an exemplary balanceassessment protocol, namely the Sensory Organization Test (“SOT”).Although, those of ordinary skill in the art will readily appreciatethat the immersive virtual reality environment of the force measurementsystem 100 can be utilized with various other assessment protocols aswell. For example, the force measurement system 100 could also includeprotocols, such as the Center of Gravity (“COG”) Alignment test, theAdaptation Test (“ADT”), the Limits of Stability (“LOS”) test, theWeight Bearing Squat test, the Rhythmic Weight Shift test, and theUnilateral Stance test. In addition, the immersive virtual realityenvironment and the displaceable force measurement assembly 102 of theforce measurement system 100 can be used with various forms of training,such as closed chain training, mobility training, quick training, seatedtraining, and weight shifting training. A brief description of each ofthese five categories of training will be provided hereinafter.

Closed chain training requires users to specify hip, knee, ankle, orlower back for target training. The training exercises associated withclosed chain training are designed to gradually increase the amount offlexibility and to increase the overall amount of difficulty.

Mobility training starts with elements from seated training andprogresses up through a full stepping motion. One goal of this trainingseries is to help a patient coordinate the sit to stand movement and tohelp the patient regain control of normal activities of daily living.

Quick Training is designed to meet the basic needs of training in aquick and easy to set up interface. A variety of different trainings canbe chosen that range from simple stand still with the cursor in thecenter target to FIG. 8 motions.

Seated training is performed while in a seated position. Seated trainingis typically performed using a twelve (12) inch block as a base togetherwith a four (4) inch block, a foam block, or a rocker board placed ontop of the twelve (12) inch block. These training exercises help asubject or patient begin to explore their base of support as well ascoordinate core stability.

Weight shifting training involves leaning or moving in four differentdirections: forward, backward, left, or right. Combined with movementson top of different surfaces, the goal of the weight shifting trainingis to get people more comfortable with moving beyond their comfortlevels through challenging them to hit targets placed close togetherinitially, and then moving them outward toward their theoretical limits.

In general, each training protocol may utilize a series of targets ormarkers that are displayed on the screen 168 of the subject visualdisplay device 107. The goal of the training is for the subject orpatient 108 to move a displaceable visual indicator (e.g., a cursor)into the stationary targets or markers that are displayed on the screen168. For example, as shown in the screen image 232 of FIG. 22, theoutput screen 168 of the subject visual display device 107 may bedivided into a first, inner screen portion 234, which comprisesinstructional information for a subject 204 performing a particular testor training protocol, and a second outer screen portion 236, whichcomprises a displaceable background or one or more virtual realityscenes that are configured to create a simulated environment for thesubject 204. As shown in FIG. 22, a plurality of targets or markers 238(e.g., in the form of circles) are displayed on the first, inner screenportion 234. In addition, a displaceable visual indicator or cursor 240is also displayed on the first, inner screen portion 234. The dataacquisition/data processing device 104 controls the movement of thevisual indicator 240 towards the plurality of stationary targets ormarkers 238 by using the one or more computed numerical valuesdetermined from the output signals of the force transducers associatedwith the force measurement assembly 102. In the illustrated embodiment,the first, inner screen portion 234 is provided with a plain whitebackground.

In an illustrative embodiment, the one or more numerical valuesdetermined from the output signals of the force transducers associatedwith the force measurement assembly 102, 102′ comprise the center ofpressure coordinates (x_(P), y_(P)) computed from the ground reactionforces exerted on the force plate assembly 102 by the subject. Forexample, with reference to the force plate coordinate axes 150, 152 ofFIG. 7, when a subject leans to the left on the force measurementassembly 102′ (i.e., when the x-coordinate x_(P) of the center ofpressure is positive), the cursor 240 displayed on the inner screenportion 234 is displaced to the left. Conversely, when a subject leansto the right on the force measurement assembly 102′ (i.e., when thex-coordinate x_(P) of the center of pressure is negative in FIG. 7), thecursor 240 on the inner screen portion 234 is displaced to the right.When a subject leans forward on the force measurement assembly 102′(i.e., when the y-coordinate y_(P) of the center of pressure is positivein FIG. 7), the cursor 240 displayed on the inner screen portion 234 isupwardly displaced on the inner screen portion 234. Conversely, when asubject leans backward on the force measurement assembly 102′ (i.e.,when the y-coordinate y_(P) of the center of pressure is negative inFIG. 7), the cursor 240 displayed on the inner screen portion 234 isdownwardly displaced on the inner screen portion 234. In the trainingscenario illustrated in FIG. 22, the subject 204 may be instructed tomove the cursor 240 towards each of the plurality of targets or markers238 in succession. For example, the subject 204, may be instructed tomove the cursor 240 towards successive targets 238 in a clockwisefashion (e.g., beginning with the topmost target 238 on the first, innerscreen portion 234).

As illustrated in FIG. 22, a virtual reality scenario is displayed onthe second outer screen portion 236 of the output screen 168 of thesubject visual display device 107. The virtual reality scenario in FIG.22 comprises a three-dimensional checkerboard room. As shown in FIG. 22,the three-dimensional checkerboard room comprises a plurality ofthree-dimensional boxes or blocks 205 in order to give the subject 204 aframe of reference for perceiving the depth of the room (i.e., the boxesor blocks 205 enhance the depth perception of the subject 204 withregard to the virtual room). In one or more embodiments, the dataacquisition/data processing device 104 is configured to generate amotion profile for the selective displacement of the virtual realityscenario. The data acquisition/data processing device 104 may generatethe motion profile for the virtual reality scenario (e.g., thethree-dimensional checkerboard room) in accordance with any one of: (i)a movement of the subject on the force measurement assembly (e.g., byusing the center of pressure coordinates (x_(P), y_(P))), (ii) adisplacement of the force measurement assembly 102 by one or moreactuators (e.g., by using the motor positional data and/or torque fromthe first and second actuator assemblies 158, 160), and (iii) apredetermined velocity set by a system user (e.g., the virtual realityscenario may be displaced inwardly at a predetermined velocity, such as5 meters per second). In an alternative embodiment, the subject could beinstructed to adapt to a pseudorandom movement of the displaceable forcemeasurement assembly 102 and/or the pseudorandom movement of the virtualreality scenario. Displacing the virtual reality scene inwardly on thevisual display device 107 inhibits the sensory ability, namely thevisual flow, of the subject by creating artificial visual inputs fromwhich he or she must differentiate from his or her actual surroundings.

In other embodiments, rather than comprising a virtual reality scenario,the second outer screen portion 236 of the output screen 168 maycomprise a displaceable background (e.g., a background comprising aplurality of dots). For either the virtual reality scenario or thedisplacement background, the data acquisition/data processing device 104is configured to displace the image displayed on the outer screenportion 236 using a plurality of different motion profiles. For example,when a displaceable background is displayed in the outer screen portion236, the displaceable background may be displaced, or scrolled,left-to-right, right-to-left, top-to-bottom, or bottom-to-top on theoutput screen 168. In addition, the data acquisition/data processingdevice 104 may be configured to rotate the displaceable background abouta central axis in any of the pitch, roll, or yaw direction (i.e., anaxis passing centrally through the output screen 168, such as alongradius line R1 in FIG. 10, rotation in the roll direction). Moreover,the data acquisition/data processing device 104 may be configured toadjust the position of the central axis, about which the displaceablebackground rotates, based upon a subject height input value so that thecentral axis is approximately disposed at the eye level of the subject.It is to be understood that any of these motion profiles described inconjunction with the displaceable background also can be applied to thevirtual reality scenario by the data acquisition/data processing device104. Preferably, the data acquisition/data processing device 104 is alsospecially programmed so as to enable a system user (e.g., a clinician)to selectively choose the manner in which the displaceable background isdisplaced during the training routines (i.e., the data acquisition/dataprocessing device 104 is preferably provided with various setup optionsthat allow the clinician to determine how the displaceable backgroundmoves during the training routines described herein). Also, preferably,the data acquisition/data processing device 104 is specially programmedso as to enable a system user (e.g., a clinician) to selectively choosefrom a plurality of different displaceable backgrounds that can beinterchangeably used during various training routines.

In FIG. 22, the inner screen portion 234 is depicted with a border 242,which separates the inner screen portion 234 from the second outerscreen portion 236. However, it is to be understood that, in otherembodiments of the invention, the border 242 may be omitted. Also, insome embodiments, the data acquisition/data processing device 104 isspecially programmed so as to enable a system user (e.g., a clinician)to selectively choose whether or not the inner screen portion 234 withthe patient instructional information displayed thereon is displaced inaccordance with the movement of the subject on the displaceable forcemeasurement assembly 102.

In another embodiment, with reference to FIG. 23, it can be seen thatonly instructional information for a subject 204 may be displayed on theoutput screen 168 of the subject visual display device 107. As shown inthis figure, a plurality of enlarged targets or markers 238′ (e.g., inthe form of circles) and an enlarged displaceable visual indicator orcursor 240′ are displayed on the output screen 168. As described above,during the execution of the training protocol, the subject 204 isinstructed to move the cursor 240′ into each of the plurality targets ormarkers 238′ in successive progression. In FIG. 23, the plurality oftargets or markers 238′ and the displaceable visual indicator or cursor240′ are displaced on a plain white background that is not moving.

In yet another embodiment, the configuration of the output screen 168 ofthe subject visual display device 107 could be similar to that which isdepicted in FIG. 22, except that the plurality of targets or markers 238and the displaceable visual indicator or cursor 240 could besuperimposed directly on the displaceable background, rather than beingseparated therefrom in the inner screen portion 234. Thus, unlike inFIG. 22, where the targets 238 and the cursor 240 are superimposed on aplain white background, the targets 238 and the cursor 240 would bedisplayed directly on the displaceable background. In some scenarios,the targets 238 would be stationary on the output screen 168 of thesubject visual display device 107, while in other scenarios, the targets238 could be displaced on the output screen 168 of the subject visualdisplay device 107 while the subject 204 is undergoing training.

In still another embodiment, the data acquisition/data processing device104 is specially programmed with a plurality of options that can bechanged in order to control the level of difficulty of the training.These options may include: (i) pacing (i.e., how fast a patient mustmove from target 238, 238′ to target 238, 238′), (ii) the percentage oflimits of stability (which changes the spacing of the targets 238, 238′,(iii) percent weight bearing (i.e., the targets 238, 238′ can beadjusted in accordance with the percentage of a subject's weight that istypically placed on his or her right leg as compared to his or her leftleg so as to customize the training for a particular subject, i.e., toaccount for a disability, etc.), and (iv) accessories that can placed onthe plate surface (i.e., type of surface to stand on (e.g., solid orfoam), size of box to step on/over, etc.). In addition, the dataacquisition/data processing device 104 can be specially programmed toadjust the magnitude of the response of the displaceable forcemeasurement assembly 102 and the virtual reality environment on thescreen 168. For example, while a subject is undergoing training on thesystem 100, the displacement of the virtual reality environment on thescreen 168 could be set to a predetermined higher or lower speed.Similarly, the speed of rotation and/or translation of the displaceableforce measurement assembly 102 could be set to predetermined higher orlower speed.

In yet another embodiment, the data acquisition/data processing device104 is configured to compute the vertical forces F_(Lz), F_(Rz) exertedon the surface of the first and second force plate components 110, 112by the respective feet of the subject, or alternatively, to receivethese computed values for F_(Lz), F_(Rz) from the programmable logiccontroller 172. In this embodiment, with reference to the screen image258 of FIG. 24, first and second displaceable visual indicators (e.g.,in the form of adjacent displaceable bars 260, 262) are displayed on theoutput screen 168 of the subject visual display device 107. As shown inFIG. 24, the first displaceable bar 260 represents the percentage of asubject's total body weight that is disposed on his or her left leg,whereas the second displaceable bar 262 represents the percentage of asubject's total body weight that is disposed on his or her right leg. InFIG. 24, because this is a black-and-white image, the different colors(e.g., red and green) of the displaceable bars 260, 262 are indicatedthrough the use of different hatching patterns (i.e., displaceable bar260 is denoted using a crisscross type hatching pattern, whereasdisplaceable bar 262 is denoted using a diagonal hatching pattern). Thetarget percentage line 264 in FIG. 24 (e.g., a line disposed at 60% oftotal body weight) gives the subject 204 a goal for maintaining acertain percentage of his body weight on a prescribed leg during theperformance of a particular task. For example, the subject 204, may beinstructed to move from a sit-to-stand position while being disposed onthe dual force measurement assembly 102. While performing thesit-to-stand task, the subject 204 is instructed to maintainapproximately 60% of his or her total body weight on his or her leftleg, or alternatively, maintain approximately 60% of his or her totalbody weight on his or her right leg. During the performance of thistask, the data acquisition/data processing device 104 controls therespective positions of the displaceable bars 260, 262 using thecomputed values for the vertical forces F_(Lz), F_(Rz) (i.e., the bars260, 262 are displayed on the output screen 168 in accordance with thevalues for the vertical forces F_(Lz), F_(Rz) determined over the timeperiod of the sit-to-stand task task). If the subject is able tomaintain approximately the percentage weight goal on his or herprescribed leg, then the displaceable bar 260, 262 for that leg (eitherright or left) will continually oscillate in close proximity to thetarget percentage line 264.

For the left bar 260 displayed in FIG. 24, the percentage weight for theleft leg is computed as follows:

$\begin{matrix}{{\% W_{L}} = {\left( \frac{F_{Z_{L}}}{F_{Z_{L}} + F_{Z_{R}}} \right)*100\%}} & (2)\end{matrix}$where:% W_(L): percentage of total body weight disposed on subject's left leg;F_(Z) _(L) : vertical force on subject's left leg (e.g., in Newtons);andF_(Z) _(R) : vertical force on subject's right leg (e.g., in Newtons).For the right bar 262 displayed in FIG. 24, the percentage weight forthe right leg is computed as follows:

$\begin{matrix}{{\% W_{R}} = {\left( \frac{F_{Z_{R}}}{F_{Z_{L}} + F_{Z_{R}}} \right)*100\%}} & (3)\end{matrix}$where:% W_(R): percentage of total body weight disposed on subject's rightleg;F_(Z) _(L) :vertical force on subject's left leg (e.g., in Newtons); andF_(Z) _(R) : vertical force on subject's right leg (e.g., in Newtons).

People maintain their upright posture and balance using inputs fromsomatosensory, vestibular and visual systems. In addition, individualsalso rely upon inputs from their somatosensory, vestibular and visualsystems to maintain balance when in other positions, such as seated andkneeling positions. During normal daily activity, where dynamic balanceis to be maintained, other factors also matter. These factors are visualacuity, reaction time, and muscle strength. Visual acuity is importantto see a potential danger. Reaction time and muscle strength areimportant to be able to recover from a potential fall. During theperformance of the Sensory Organization Test (“SOT”), certain sensoryinputs are taken away from the subject in order to determine whichsensory systems are deficient or to determine if the subject is relyingtoo much on one or more of the sensory systems. For example, theperformance of the SOT protocol allows one to determine how much asubject is relying upon visual feedback for maintaining his or herbalance.

In one embodiment, the SOT protocol comprises six conditions under whicha subject is tested (i.e., six test stages). In accordance with thefirst sensory condition, a subject simply stands in stationary, uprightposition on the force plate assembly 102 with his or her eyes open.During the first condition, a stationary virtual reality scene isprojected on the generally hemispherical projection screen 168 of thesubject visual display device 107, and the force plate assembly 102 ismaintained in a stationary position. For example, the virtual realityscene displayed on the generally hemispherical projection screen 168 maycomprise a checkerboard-type enclosure or room (e.g., see FIG. 14), orsome other appropriate scene with nearfield objects (e.g., boxes orblocks 205). In the illustrated embodiment, the virtual reality scene isin the form of a three-dimensional image, and the nature of the scenewill remain consistent throughout the performance of the SOT protocol.As shown in the screen image 200 of FIG. 14, a subject 204 is disposedin an immersive virtual reality environment 202 comprising athree-dimensional checkerboard room. As shown in FIG. 14, thethree-dimensional checkerboard room comprises a plurality ofthree-dimensional boxes or blocks 205 in order to give the subject 204 aframe of reference for perceiving the depth of the room (i.e., the boxesor blocks 205 enhance the depth perception of the subject 204 withregard to the virtual room).

In accordance with the second sensory condition of the SOT protocol, thesubject is blindfolded so that he or she is unable to see thesurrounding environment. Similar to the first condition, the force plateassembly 102 is maintained in a stationary position during the secondcondition of the SOT test. By blindfolding the subject, the secondcondition of the SOT effectively removes the visual feedback of thesubject.

During the third condition of the SOT protocol, like the first andsecond conditions, the force plate assembly 102 remains in a stationaryposition. However, in accordance with the third sensory condition of thetest, the virtual reality scene displayed on the generally hemisphericalprojection screen 168 is moved in sync with the sway angle of thesubject disposed on the force plate assembly 102. For example, when thesubject leans forward on the force plate assembly 102, the virtualreality scene displayed on the screen 168 is altered so as to appear tothe subject to be inwardly displaced on the output screen 168.Conversely, when the subject leans backward on the force plate assembly102, the virtual reality scene is adjusted so as to appear to thesubject to be outwardly displaced on the screen 168. As in the firstcondition, the eyes of the subject remain open during the thirdcondition of the SOT protocol.

In accordance with the fourth sensory condition of the SOT protocol, theforce plate assembly 102 and the subject disposed thereon is displaced(e.g., rotated), while the eyes of the subject remain open. The forceplate assembly 102 is displaced according to the measured sway angle ofthe subject (i.e., the rotation of the force plate assembly 102 issynchronized with the computed sway angle of the subject). During thefourth condition, similar to the first condition, a stationary virtualreality scene is projected on the generally hemispherical projectionscreen 168 of the subject visual display device 107.

During the fifth condition of the SOT protocol, like the secondcondition thereof, the subject is blindfolded so that he or she isunable to see the surrounding environment. However, unlike during thesecond condition, the force plate assembly 102 does not remainstationary, rather the force plate assembly 102 and the subject disposedthereon is displaced (e.g., rotated). As for the fourth condition, theforce plate assembly 102 is displaced according to the measured swayangle of the subject (i.e., the rotation of the force plate assembly 102is synchronized with the computed sway angle of the subject). As wasdescribed above for the second condition of SOT protocol, byblindfolding the subject, the fifth condition of the SOT testeffectively removes the visual feedback of the subject.

Lastly, during the sixth sensory condition of the SOT protocol, like thefourth and fifth conditions, the force plate assembly 102 and thesubject disposed thereon is displaced (e.g., rotated). Although, inaccordance with the sixth sensory condition of the test, the virtualreality scene displayed on the generally hemispherical projection screen168 is also moved in sync with the sway angle of the subject disposed onthe force plate assembly 102. As previously described for the fourth andfifth conditions, the displacement of the force plate assembly 102 isgoverned by the measured sway angle of the subject (i.e., the rotationof the force plate assembly 102 is synchronized with the computed swayangle of the subject). In an exemplary embodiment, when the subject isforwardly displaced on the force plate assembly 102 during the sixthcondition of the SOT protocol, the virtual reality scene displayed onthe screen 168 is altered so as to appear to the subject to be inwardlydisplaced on the output screen 168. Conversely, when the subject isrearwardly displaced on the force plate assembly 102, the virtualreality scene is adjusted so as to appear to the subject to be outwardlydisplaced on the screen 168. As in the fourth condition, the eyes of thesubject remain open during the sixth condition of the SOT protocol.

During the performance of the SOT protocol, the scene or screen imagedisplayed on the generally hemispherical projection screen 168 may alsocomprise one of the images illustrated in FIGS. 47 and 48. Initially,turning to FIG. 47, it can be seen that the screen image 276 on thehemispherical projection screen 168 comprises a plurality ofsubstantially concentric bands 278 that are configured to create adisorienting visual stimuli for the subject disposed on the forcemeasurement assembly 102. The specially programmed data acquisition/dataprocessing device 104 of the force measurement system 100 generates thescreen image 276 of FIG. 47, and the projector 164″ projects thegenerated image onto the screen 168. As depicted in FIG. 47, it can beseen that each of the plurality of substantially concentric bands 278comprise blurred edge portions without any clearly defined boundarylines so that the subject is unable to establish a particular focalpoint of reference on the output screen 168. In other words, each bandor ring 278 comprises a gradient-type edge portion 280 that is verydiffuse in nature, and does not comprise any hard line transitions. Asshown in FIG. 47, the plurality of substantially concentric bands 278generated by the specially programmed data acquisition/data processingdevice 104 of the force measurement system 100 are three-dimensionallyarranged on the screen 168 so as to create a three-dimensional tunneleffect for the subject. Advantageously, because the blurred orgradient-type edge portions 280 of the band or rings 278 do not includeany clearly defined boundary lines or fixation points, the subject isunable to establish a particular focal point of reference on the outputscreen 168. When a subject is performing conditions three and six of theSOT protocol, it is desired that the subject believe that he or she isnot moving, when in fact, he or she is actually moving on the surface ofthe force measurement assembly 102. Advantageously, the absence of allhard lines and defined points in the screen image 276 of FIG. 47eliminates the frame of reference that the subject would otherwiseutilize to visually detect their movement on the force measurementassembly 102, and thus greatly enhances the effectiveness of the SOTprotocol. The screen image 276 of FIG. 47 enhances the effectiveness ofthe SOT protocol by precluding the visual input normally available froma defined reference point or line on the screen in front of the subject.

While each of the bands or rings 278 in the screen image 276 of FIG. 47is generally circular in shape, it is to be understood that theinvention is not so limited. Rather, other suitable shapes may be usedfor the bands or rings 278 as well. For example, in other embodiments ofthe invention, the bands or rings generated by the one or more dataprocessing devices, and projected on the hemispherical projection screen168, may comprise one or more of the following other configurations: (i)a plurality of elliptical concentric bands or rings, (ii) a plurality ofrectangular concentric bands or rings, (iii) a plurality of squareconcentric bands or rings, and (iv) a plurality of concentric bands orrings having generally straight side portions with rounded cornerportions.

In an exemplary embodiment, when the plurality of concentric bands orrings have generally straight side portions with rounded cornerportions, the straight side portion of each band or ring may compriseone-third (⅓) of its overall height or width, while the radius of eachrounded corner portion may comprise one-third (⅓) of its overall heightor width. As such, in the exemplary embodiment, the straight sideportion of each band or ring comprises one-third (⅓) of its overallheight or width, the first rounded corner portion comprises one-third(⅓) of its overall height or width, and the second rounded cornerportion comprises the remaining one-third (⅓) of its overall height orwidth. However, in other embodiments, it is to be understood thatstraight side portions and the rounded corner portions may compriseother suitable ratios of the overall height or width of band or rings.

Next, turning to FIG. 48, it can be seen that the screen image 276′ onthe hemispherical projection screen 168 comprises a plurality ofsubstantially concentric bands 278′, which are similar in many respectsto those depicted in FIG. 47, except that the bands 278′ in FIG. 48 havea different overall shape. In particular, the plurality of concentricbands or rings 278′ in FIG. 48 are generally elliptical or oval inshape, rather than circular in shape. As was described above for theimage 276 of FIG. 47, the data acquisition/data processing device 104 ofthe force measurement system 100 is specially programmed to generate thescreen image 276′ of FIG. 48, and the projector 164″ projects thegenerated image onto the screen 168. Like the bands or rings 278 of FIG.47, the concentric bands or rings 278′ of FIG. 48 also comprisegradient-type edge portions 280′ without any clearly defined boundarylines so that the subject is unable to establish a particular focalpoint of reference on the output screen 168. In addition, thesubstantially concentric bands 278′ of FIG. 48 are three-dimensionallyarranged on the screen 168 so as to create a three-dimensional tunneleffect for the subject. As was explained above for the screen image ofFIG. 47, the absence of all hard lines and defined points in the screenimage 276′ of FIG. 48 eliminates the frame of reference that the subjectwould otherwise utilize to visually detect their movement on the forcemeasurement assembly 102, and thus greatly enhances the effectiveness ofthe SOT protocol. In some embodiments, the concentric bands 278′ in FIG.48 are provided with an elliptical or oval shape in order to emulate apassageway of a building (i.e., so the subject viewing the screen image276′ has the illusion that he or she is traveling down a hallway orpassageway of a building). Also, in some embodiments, the screen image276′ of FIG. 48, as well as the screen image 276 of FIG. 47, is rotatedabout a central axis in any one of the pitch, roll, or yaw direction(i.e., an axis passing centrally through the output screen 168, such asalong radius line R1 in FIG. 10, rotation in the roll direction) duringthe performance of the SOT protocol. The movement of the screen image276, 276′ may also be synchronized with the movement of the subject suchthat the screen image 276, 276′ is rotated and inwardly or outwardlydisplaced on the screen in sync with a sway angle of the subject (e.g.,when the subject leans forward on the force plate, the image is rotateddownwardly and displaced into the screen, and is oppositely displacedwhen the subject leans backward of the force plate).

Referring again to FIG. 48, it can be seen that the screen image 276′also comprises a horizontal line 282 disposed laterally across theplurality of concentric bands or rings 278′. That is, the horizontalline 282 laterally intersects the plurality of concentric bands or rings278′. As shown in FIG. 48, the horizontal line 282 is disposed closer tothe top of each elliptically-shaped band or ring 278′, than the bottomof each elliptically-shaped band or ring 278′, so as to be generallyaligned with the line of sight of a subject of average height. In one ormore embodiments, the horizontal line 282 is utilized as a visualreference line for the subject during the performance of conditions one,two, four, and five of the SOT protocol (i.e., the conditions of the SOTprotocol during which the screen image on the hemispherical projectionscreen 168 is not displaced). In these one or more embodiments, thehorizontal line 282 is configured to be selectively turned on and off bythe specially programmed data acquisition/data processing device 104 ofthe force measurement system 100 so that it is capable of beingdisplayed during conditions one, two, four, and five of the SOT protocol(i.e., when the screen image is not displaced), but then turned offduring conditions three and six of the SOT protocol (i.e., when thescreen image is displaced).

In addition, while the screen images 276, 276′ of FIGS. 47 and 48 areparticularly suitable for use in the SOT protocol, it is to beunderstood that these the screen images 276, 276′ may be utilized inconjunction with other balance and postural stability tests andprotocols as well. For example, the screen images 276, 276′ of FIGS. 47and 48 may also be employed in the Adaptation Test (“ADT”) and the MotorControl Test (“MCT”), while testing the balance of a subject or patient.

In another embodiment, the data acquisition/data processing device 104of the force measurement system 100 may be specially programmed toexecute a modified version of the SOT protocol wherein two or more ofthe six conditions of the protocol are combined with one another so asto more accurately and efficiently perform the test. The SOT protocoldescribed above comprises six separate conditions (i.e., discretesub-tests), each of which are performed for a predetermined period oftime (e.g., each of the six conditions of the SOT protocol may beperformed for approximately 20 seconds). In the modified version of theSOT protocol that will be described hereinafter, the displacementvelocity (e.g., gain) of the screen background image is graduallyincremented over time by the data acquisition/data processing device 104from an initial static condition to a final dynamic condition. At thefinal dynamic condition, the screen image on the hemisphericalprojection screen 168 is displaced at a velocity that is equal to, orgreater than the subject's movement (e.g., the displacement velocity ofthe screen image may be synchronized with the subject's computed swayangle velocity or it may be greater than the subject's sway anglevelocity). Rather than the plurality of discrete conditions or sub-teststhat are utilized in the SOT protocol explained above, the modifiedversion of the SOT protocol that will be described hereinafter utilizesa continuum of different test conditions that continually vary over thetime duration of the SOT protocol. Advantageously, the modified protocolallows the SOT testing to be performed more efficiently because, if itis determined that the subject is successfully performing the protocolas the velocity of the screen image is continually increased, thetesting can simply be stopped after a shorter period (i.e., the test maybe able to be stopped after 20 seconds, 30 seconds, etc.).

The modified version of the SOT protocol may initially comprisegenerating, by using the specially programmed data acquisition/dataprocessing device 104 of the force measurement system 100, one or morescreen images (e.g., screen images 276, 276′) that are displayed on thehemispherical projection screen 168. At the commencement of the SOTprotocol, the one or more screen images are displayed on the outputscreen 168 in an initial static condition wherein the one or more imagesare generally stationary (i.e., the images are not moving on the screen168). Subsequent to the initial static condition, the one or more imagesare displaced on the output screen 168 in accordance with a velocityvalue that incrementally increases over time as the SOT protocolprogresses (e.g., the velocity value of the one or more images may beincremented by a predetermined amount every five (5) seconds so that thevelocity value gets progressively higher as the SOT protocolprogresses). The displacement of the one or more images on the outputscreen 168 may comprise, for example, left-to-right displacement,right-to-left displacement, top-to-bottom displacement, and/orbottom-to-top displacement on the screen 168. The displacement of theone or more images on the output screen 168 also may comprisedisplacements corresponding to: (i) a medial-lateral direction of thesubject, (ii) an anterior-posterior direction of the subject, and/or(iii) a superior-inferior direction of the subject. In addition, thedata acquisition/data processing device 104 of the force measurementsystem 100 may be specially programmed to rotate the displaceableimage(s) about a central axis in any of the pitch, roll, or yawdirection (i.e., an axis passing centrally through the output screen168, such as along radius line R1 in FIG. 10, rotation in the rolldirection) during the SOT protocol. As such, the image velocity valuethat is incrementally increased during the modified SOT protocol maycomprise a linear velocity value or an angular velocity value. While themodified SOT protocol is being performed, and the screen image isgradually being displaced at an incrementally higher velocity, theperformance of the subject or patient is evaluated in order to assess apostural stability of the subject (e.g., by evaluating the subject'scenter-of-pressure, center-of-gravity, and/or sway angle over time).

As an alternative to displacing one or images on the screen 168 duringthe performance of the modified SOT protocol, it is to be understoodthat a displaceable visual surround device, which at least partiallycircumscribes three sides of a subject (i.e., three sides of a torso ofa subject), may be employed. In particular, with reference to FIG. 46,the visual surround device 191 may comprise visual surround portion 192that is displaceable by means of one or more actuators in an actuatordevice 193 that are operatively coupled to the specially programmed dataacquisition/data processing device 104 of the force measurement system100. In this alternative embodiment, the one or more data processingdevices generate a motion profile for the visual surround device 191,rather than generating a motion profile for a displaceable image on thescreen 168. At the commencement of the SOT protocol, the visual surroundportion 192 of the visual surround device 191 is maintained in aninitial static condition wherein the visual surround portion 192 isgenerally stationary. Subsequent to the initial static condition, thevisual surround portion 192 is displaced by the one or more actuators inthe actuator device 193 in accordance with a velocity value thatincrementally increases over time as the SOT protocol progresses (e.g.,the displacement velocity value of the visual surround portion 192 maybe incremented by a predetermined amount every five (5) seconds so thatthe velocity value gets progressively higher as the SOT protocolprogresses). Similar to that which was described above for thedisplaceable screen images, the displacement the visual surround portion192 may comprise, for example, left-to-right displacement, right-to-leftdisplacement, top-to-bottom displacement, and/or bottom-to-topdisplacement, depending on the quantity and the placement of theactuators. The displacement of the visual surround portion 192 also maycomprise displacements corresponding to: (i) a medial-lateral directionof the subject, (ii) an anterior-posterior direction of the subject,and/or (iii) a superior-inferior direction of the subject. In addition,the data acquisition/data processing device 104 of the force measurementsystem 100 may be specially programmed to rotate the visual surroundportion 192 about a central axis in any of the pitch, roll, or yawdirection (i.e., an axis passing centrally through the visual surroundportion 192, rotation in the roll direction) during the SOT protocol. Assuch, as was described above for the displaceable screen images, thevelocity value of the visual surround portion 192 that is incrementallyincreased during the modified SOT protocol may comprise a linearvelocity value or an angular velocity value. While the modified SOTprotocol is being performed, and the visual surround portion 192 isgradually being displaced at an incrementally higher velocity, theperformance of the subject or patient is evaluated in order to assess apostural stability of the subject (e.g., by evaluating the subject'scenter-of-pressure, center-of-gravity, and/or sway angle over time).Referring again to FIG. 46, it can be seen that, in the illustratedembodiment, the visual surround portion 192 is rotationally displaced(i.e., as indicated by curved arrows 194) about a transverse horizontalaxis TA_(VS).

Similar to that described above for the displacement of the screenimage, the displacement velocity (e.g., gain) of the visual surroundportion 192 may be gradually incremented over time from an initialstatic condition to a final dynamic condition. At the final dynamiccondition, the visual surround portion 192 is displaced at a velocitythat is equal to, or greater than the subject's movement (e.g., thedisplacement velocity of the visual surround portion 192 may besynchronized with the subject's computed sway angle velocity or it maybe greater than the subject's sway angle velocity). For example, in theillustrated embodiment of FIG. 46, the angular velocity of the visualsurround portion 192 about the transverse axis TA_(VS) may be equal tothe subject's sway angle velocity at the final dynamic condition.

In the modified SOT protocol, the force measurement assembly 102, andthe subject disposed thereon, may be incrementally displaced in a mannersimilar to that described above for the screen image on the screen 168and the visual surround portion 192. That is, the second actuatorassembly 160 may be used to rotate the force measurement assembly 102,and the subject disposed thereon, at an incrementally higher angularvelocity during the modified SOT protocol (see FIG. 2). At thecommencement of the SOT protocol, the force measurement assembly 102,and the subject disposed thereon, are maintained in an initial staticcondition wherein the force measurement assembly 102 and the subject arestationary. Subsequent to the initial static condition, the forcemeasurement assembly 102, and the subject disposed thereon, are rotatedin accordance with a velocity value that incrementally increases overtime as the SOT protocol progresses (e.g., the angular velocity value ofthe force measurement assembly 102 and the subject may be incremented bya predetermined amount every five (5) seconds so that the velocity valuegets progressively higher as the SOT protocol progresses). While themodified SOT protocol is being performed, and the force measurementassembly 102 carrying the subject is gradually being displaced at anincrementally higher angular velocity, the performance of the subject orpatient is evaluated in order to assess a postural stability of thesubject (e.g., by evaluating the subject's center-of-pressure,center-of-gravity, and/or sway angle over time).

Similar to that described above for the displacement of the screen imageand the visual surround portion 192, the rotational velocity (e.g.,gain) of the force measurement assembly 102 carrying the subject may begradually incremented over time from an initial static condition to afinal dynamic condition. At the final dynamic condition, the forcemeasurement assembly 102 carrying the subject is displaced at an angularvelocity that is equal to, or greater than the subject's movement (e.g.,the displacement velocity of the screen image may be synchronized withthe subject's computed sway angle velocity or it may be greater than thesubject's sway angle velocity). During the performance of the modifiedSOT protocol, the displacement velocity of either the screen image orthe visual surround portion 192 may be generally equal to the angulardisplacement velocity of the force measurement assembly 102 and thesubject (i.e., the force measurement assembly 102 and the subjectdisposed thereon may be displaced using an angular velocity that issynchronized with the displacement velocity of either the screen imageor the visual surround portion 192).

Advantageously, because the velocity of the screen image, the visualsurround portion 192, and/or the force measurement assembly 102 carryingthe subject are incrementally increased during the performance of themodified SOT protocol, the SOT protocol is capable of being performed ina far more efficient manner. That is, rather than laboriously executingsix separate conditions for fixed time durations, the protocolconditions are combined with one another so that it takes far less timeto determine the actual performance of the subject. In one or moreembodiments, the data acquisition/data processing device 104 of theforce measurement system 100 may be specially programmed to determinethe time duration of the SOT protocol in accordance with a quasireal-time assessment of the postural stability of the subject (e.g., byevaluating the subject's center-of-pressure, center-of-gravity, and/orsway angle over time). As such, when an accurate assessment of thesubject's performance is obtained, the modified SOT protocol is simplyconcluded.

As explained above, the modified version of the SOT protocol combinestwo or more conditions with one another so as to more accurately andefficiently perform the test. For example, the first SOT conditiondescribed above may be combined with the third SOT condition. Similarly,the fourth SOT condition described above may be combined with the sixSOT condition, while the second condition (blindfolded subject,stationary force measurement assembly 102) may be combined with thefifth SOT condition (blindfolded subject, displaced force measurementassembly 102). Also, in some embodiments, three conditions of the SOTprotocol may be combined with one another. For example, the first,third, and sixth conditions of the SOT protocol may be combined with oneanother so that either the displacement velocity of the screen image orvisual surround portion 192 is simultaneously incremented together withthe angular displacement velocity of the force measurement assembly 102and the subject disposed thereon. In one exemplary embodiment of themodified SOT protocol, the combined first, third, and sixth conditionsof the SOT protocol may be performed initially, and then the combinedsecond and fifth conditions may be performed thereafter. Also, becausethe subject's performance is evaluated in quasi real-time during theperformance of the modified SOT protocol, the data acquisition/dataprocessing device 104 of the force measurement system 100 may bespecially programmed so as to automatically combine different sequencesof conditions with one another based upon the subject's performanceduring the modified SOT protocol. Also, the data acquisition/dataprocessing device 104 of the force measurement system 100 may bespecially programmed so as to allow the system operator (e.g., aclinician) to select different conditions to be combined with oneanother while the subject or patient is executing the modified SOTprotocol. That is, the system operator may monitor the subject'sperformance during the execution of the modified SOT protocol, and thenselect a particular sequence of conditions based upon that performance.

During the performance of the modified SOT protocol, it is to beunderstood that the screen images 276, 276′, which were described inconjunction with FIGS. 47 and 48 above, may be displayed on thegenerally hemispherical projection screen 168 while one or more of theconditions are being performed. For example, the screen images 276, 276′of FIGS. 47 and 48 may be utilized during the performance of anycombination of the first, third, fourth, and sixth conditions.

Also, in one or more alternative embodiments, during the performance ofthe balance test (e.g., the SOT protocol or modified SOT protocoldescribed above), the subject or patient 108 may be outfitted withaugmented reality glasses (i.e., reality-altering glasses) in order toperturb the subject's visual input during the performance of the balancetest. For example, in these embodiments, the screen images 276, 276′ ofFIGS. 47 and 48 may be displayed using the augmented reality glasses(i.e., reality-altering glasses), rather than on the generallyhemispherical projection screen 168. The augmented reality glasses maycomprise one or more high-resolution liquid-crystal (LCD) displays(e.g., two (2) LCD displays) that generate a large virtual screen image(e.g., 60″ to 80″ virtual screen viewed from 10 feet) for the user,wherein the augmented reality glasses are capable of displaying bothtwo-dimensional (2D) and three-dimensional (3D) video for the userthereof. The augmented reality glasses may further comprise one or morediscrete video graphics array (VGA) cameras (e.g., two (2) VGA cameras)for capturing both two-dimensional (2D) and three-dimensional (3D)stereoscopic video images of the environment surrounding the user. Inaddition, the augmented reality glasses may comprise an inertialmeasurement unit (IMU) integrated therein, which comprises three (3)accelerometers, three (3) gyroscopes, and three (3) magnetometers fortracking the head movement of the user so that the user's current headdirection and angle of view may be determined. Also, the augmentedreality glasses may comprise one or more interfaces (e.g.,high-definition multimedia interface (HDMI) or a suitable wirelessinterface) that operatively connect the augmented reality glasses to anexternal data processing device (e.g., data acquisition/data processingdevice 104 or 330). It is to be understood that the augmented realityglasses worn by the subject or patient 108 during the performance of abalance test (e.g., the SOT protocol or modified SOT protocol) couldachieve the same effect described above with regard to the images ofFIGS. 47 and 48. Also, the augmented reality glasses may be worn by thesubject or patient 108 while performing the modified SOT protocoldescribed above so that the one or more images, which are displaced atincrementally higher velocities during the performance of the protocol,are displaced on a virtual output screen projected in front of thesubject.

Also, in one or more alternative embodiments, the reality-alteringglasses worn by the subject or patient 108 may be designed such that thesubject or patient 108 has no direct view of the surroundingenvironment. That is, the only view that the subject or patient 108 hasof the surrounding environment is the view projected on the one or morevisual display devices of the reality-altering glasses (i.e., thereality-altering glasses may be in the form of virtual reality glasses).

In these one or more alternative embodiments, the data acquisition/dataprocessing device 330 may be specially programmed to alter, displace, orboth alter and displace one or more video images of an environmentsurrounding the subject so that, when the one or more video images aredisplayed to the subject on the one or more visual displays of theaugmented reality glasses, the one or more video images no longer depictan accurate representation of the environment surrounding the subject soas to perturb a visual input of the subject. For example, the dataacquisition/data processing device 330 may be specially programmed tolaterally, vertically, or rotationally displace the images of theenvironment surrounding the subject so that, when they are viewed by thesubject using the one or more visual displays of the augmented realityglasses, the images of the environment are skewed relative to the actualenvironmental setting. As such, after being altered by the dataacquisition/data processing device 330, the images of the environmentsurrounding the subject, as viewed by the subject through the augmentedreality glasses, are visually distorted relative to the actualenvironment that the subject would see if he or she were lookingdirectly at the environment and not wearing the augmented realityglasses. Thus, the manipulation of the images of the environment by thedata acquisition/data processing device 330 results in the conveyance ofa distorted view of reality to the subject, thereby perturbing thevisual input of the subject.

In addition, in one or more alternative embodiments, it is to beunderstood that the augmented reality glasses may be used alone toperturb the subject's visual input, or in combination with a forcemeasurement assembly (e.g., force measurement assembly 102 describedherein). For example, the augmented reality glasses may be used toperturb the subject's visual input while the subject 108 issimultaneously displaced on the force measurement assembly 102 duringthe performance of a balance test, such as the SOT protocol or modifiedSOT protocol described herein.

In these one or more alternative embodiments, the data acquisition/dataprocessing device 330 may also be specially programmed to perform thefunctionality that is illustrated in FIGS. 51A-51C. Initially, withreference to FIG. 51A, it can be seen that a subject 108 wearingaugmented reality glasses 326 is disposed on a force measurementassembly 102′ (i.e., a force plate) in a generally upright position(i.e., so that a vertical reference axis passing through the subject 108is perpendicular to the top surface of the force plate 102). In theconfiguration of FIG. 51A, the screen image 332 that is viewed by thesubject 108 through the augmented reality glasses 326 matches the actualview of the scenery 334 that is captured by the one or more cameras 328of the augmented reality glasses 326. That is, in FIG. 51A, the scenerythat is disposed in front of the one or more cameras 328 of theaugmented reality glasses 326, and in front of the subject 108, is notaltered by the data acquisition/data processing device 330 that isoperatively coupled to the augmented reality glasses 326. A referenceline 340 is superimposed on each of the screen images 334, 336, 338 inFIGS. 51A, 51B, 51C in order to more clearly illustrate the manner inwhich the image captured by the camera 328 is shifted when the subject108 is in the sway angle θ₁, θ₂ positions on the force plate 102′.

Next, turning to FIG. 51B, it can be seen that the subject 108 who iswearing the augmented reality glasses 326 and is disposed on the forcemeasurement assembly 102′ (i.e., a force plate) is disposed in arearwardly inclined sway angle position. That is, as illustrated in FIG.51B, the longitudinal reference axis passing through the subject 108 isdisposed at a rearward angle θ₂ relative to a vertical reference axisthat is disposed perpendicular to the force plate top surface. In theconfiguration of FIG. 51B, the screen image 332 that is viewed by thesubject 108 through the augmented reality glasses 326 does not match theactual view of the scenery 336 that is captured by the one or morecameras 328 of the augmented reality glasses 326. Rather, in thescenario illustrated by FIG. 51B, the data acquisition/data processingdevice 330 that is operatively coupled to the augmented reality glasses326 is specially programmed to alter the actual view captured by the oneor more cameras 328 of the augmented reality glasses 326 so that subject108 sees the exact same view through the glasses 326 that he would seeif he were standing in a straight upright position on the force plate102′ (i.e., in the standing position of FIG. 51A). As such, by using thedata acquisition/data processing device 330 to alter the actual view ofthe surrounding scenery that is captured by the one or more cameras 328of the augmented reality glasses 326, the augmented reality systemcreates the illusion to the subject 108 that he has not moved at all(i.e., the subject's visual sense of perception is altered so that he isunable to perceive that he is disposed in a rearwardly inclinedposition). In the scenario of FIG. 51B, in order to make the screenimage 332 that is viewed by the subject 108 through the augmentedreality glasses 326 match the upright position image of FIG. 51A, thedata acquisition/data processing device 330 is specially programmed toslightly enlarge and downwardly rotate the actual view of the scenerycaptured by the one or more cameras 328 of the augmented reality glasses326 so as to correct for the rearwardly inclined orientation of thesubject 108. In the FIG. 51B scenario, in order to determine themagnitude of the magnification and the downward rotation angle of theactual view of the scenery captured by the one or more cameras 328, thedata acquisition/data processing device 330 may initially determine thecenter of pressure (COP) for the subject 108 from the force measurementassembly 102′. Then, in the manner described above, the dataacquisition/data processing device 330 may determine the center ofgravity (COG) for the subject based upon the center of pressure. Afterwhich, the sway angle θ₂ may be determined for the subject 108 using thecenter of gravity (COG) in the manner described above (e.g., seeequation (1) above). Finally, once the sway angle θ₂ is determined forthe subject 108, the displacement angle and magnification of the imageof the surrounding environment displayed to the subject 108 using theaugmented reality or reality-altering glasses 326 may be determinedusing geometric relationships between the sway angle θ₂ of the subject108 and the displacement angle of the video image of the surroundingenvironment captured by the one or more cameras 328 of thereality-altering glasses 326 (e.g., the sway angle θ₂ of the subject 108is generally equal to the displacement angle of the video image).

In an alternative embodiment, rather than enlarging and downwardlyrotating the actual view of the scenery captured by the one or morecameras 328 of the reality-altering glasses 326, the dataacquisition/data processing device 330 is specially programmed tocapture an initial image of the environment surrounding the subjectbefore the subject displaces his or her body into the rearwardlyinclined sway angle position (i.e., while the subject is still standingin a straight upright position of FIG. 51A). Then, once the subject hasdisplaced his or her body into the rearwardly inclined sway angleposition of FIG. 51B, the data acquisition/data processing device 330 isspecially programmed to display the initial image to the subject usingthe one or more visual displays of the reality-altering glasses 326 soas to create the illusion to the subject 108 that he or she is still inthe straight upright position of FIG. 51A.

Next, turning to FIG. 51C, it can be seen that the subject 108 who iswearing the augmented reality glasses 326 and is disposed on the forcemeasurement assembly 102′ (i.e., a force plate) is disposed in aforwardly inclined sway angle position. That is, as illustrated in FIG.51C, the longitudinal reference axis passing through the subject 108 isdisposed at a forward angle θ₁ relative to a vertical reference axisthat is disposed perpendicular to the force plate top surface. In theconfiguration of FIG. 51C, the screen image 332 that is viewed by thesubject 108 through the augmented reality glasses 326 does not match theactual view of the scenery 338 that is captured by the one or morecameras 328 of the augmented reality glasses 326. Rather, in thescenario illustrated by FIG. 51C, the data acquisition/data processingdevice 330 that is operatively coupled to the augmented reality glasses326 is specially programmed to alter the actual view captured by the oneor more cameras 328 of the augmented reality glasses 326 so that subject108 sees the exact same view through the glasses 326 that he would seeif he were standing in a straight upright position on the force plate102′ (i.e., in the standing position of FIG. 51A). As such, as describedabove with respect to FIG. 51B, by using the data acquisition/dataprocessing device 330 to alter the actual view of the surroundingscenery that is captured by the one or more cameras 328 of the augmentedreality glasses 326, the augmented reality system creates the illusionto the subject 108 that he has not moved at all (i.e., the subject'svisual sense of perception is altered so that he is unable to perceivethat he is disposed in a forwardly inclined position). In the scenarioof FIG. 51C, in order to make the screen image 332 that is viewed by thesubject 108 through the augmented reality glasses 326 match the uprightposition image of FIG. 51A, the data acquisition/data processing device330 is specially programmed to slightly decrease and upwardly rotate theactual view of the scenery captured by the one or more cameras 328 ofthe augmented reality glasses 326 so as to correct for the forwardlyinclined orientation of the subject 108. In the FIG. 51C scenario,similar to that described above for the FIG. 51B scenario, in order todetermine the magnitude of the demagnification and the upward rotationangle of the actual view of the scenery captured by the one or morecameras 328, the data acquisition/data processing device 330 mayinitially determine the center of pressure (COP) for the subject 108from the force measurement assembly 102′. Then, in the manner describedabove, the data acquisition/data processing device 330 may determine thecenter of gravity (COG) for the subject based upon the center ofpressure. After which, the sway angle θ₁ may be determined for thesubject 108 using the center of gravity (COG) in the manner describedabove (e.g., see equation (1) above). Finally, once the sway angle θ₁ isdetermined for the subject 108, the displacement angle anddemagnification of the image of the surrounding environment displayed tothe subject 108 using the augmented reality or reality-altering glasses326 may be determined using geometric relationships between the swayangle θ₁ of the subject 108 and the displacement angle of the videoimage of the surrounding environment captured by the one or more cameras328 of the reality-altering glasses 326 (e.g., the sway angle θ₁ of thesubject 108 is generally equal to the displacement angle of the videoimage).

In an alternative embodiment, rather than decreasing and upwardlyrotating the actual view of the scenery captured by the one or morecameras 328 of the reality-altering glasses 326, data acquisition/dataprocessing device 330 is specially programmed to capture an initialimage of the environment surrounding the subject before the subjectdisplaces his or her body into the forwardly inclined sway angleposition (i.e., while the subject is still standing in a straightupright position of FIG. 51A). Then, once the subject has displaced hisor her body into the forwardly inclined sway angle position of FIG. 51C,the data acquisition/data processing device 330 is specially programmedto display the initial image to the subject using the one or more visualdisplays of the reality-altering glasses 326 so as to create theillusion to the subject 108 that he or she is still in the straightupright position of FIG. 51A.

Rather than using the stationary-type force measurement assembly 102′depicted in FIGS. 51A-51C, it is to be understood that, in one or moreother embodiments, the displaceable force measurement assembly 102described above may alternatively be used during the balance testdescribed above, wherein the subject's visual input is perturbed usingthe reality-altering glasses 326. In these one or more otherembodiments, because the displaceable force measurement assembly 102 ismovably coupled to the base assembly 106, the rearwardly and forwardlyinclined angular positions of the subject 108 (as shown in FIGS. 51B and51C, respectively) may be achieved by rotating the force measurementassembly 102 with the subject 108 disposed thereon in accordance with apredetermined angle to achieve the forward and rearward angulardisplacements.

Further, in one or more alternative embodiments, the subject or patient108 may be outfitted with another type of head-mounted visual displaydevice that is different than the augmented reality glasses depicted inFIGS. 51A-51C. For example, as shown in FIG. 53, the subject 108disposed on the base assembly 106 with displaceable force measurementassembly 102 may be outfitted with a head-mounted visual display device344 with an output screen that at least partially circumscribes the headof the subject 108 such that the output screen of the head-mountedvisual display device 344 engages enough of the peripheral vision of thesubject 108 such that the subject 108 becomes immersed in the simulatedenvironment created by the scenes displayed on the output screen. In oneor more embodiments, the head-mounted visual display device may comprisea virtual reality headset or an augmented reality headset that has awraparound shape in order to at least partially circumscribe the head ofthe subject 108. The base assembly 106 and the displaceable forcemeasurement assembly 102 depicted in FIG. 53 have the same constituentcomponents and functionality as described above. In the embodiment ofFIG. 53, similar to that described above, the displaceable forcemeasurement assembly 102 may be operatively connected to a programmablelogic controller (PLC) 172 and a data acquisition/data processing device104. In this embodiment, the programmable logic controller (PLC) 172and/or the data acquisition/data processing device 104 may be programmedto displace the force measurement assembly 102 so as to perturb asomatosensory or proprioceptive input of the subject 108 during theperformance of a balance test (e.g., the Sensory Organization Test, theAdaptation Test, or the Motor Control Test) or training routine whereone or more sensory inputs of the subject are modified. During theperformance of a balance test or training routine where the forcemeasurement assembly 102 is displaced, the data acquisition/dataprocessing device 104 may be further programmed to utilize the outputforces and/or moments computed from the output data of the forcemeasurement assembly 102 in order to assess a response of the subject108 to the displacement of the force measurement assembly 102. Forexample, to assess the response of the subject 108 during theperformance of the balance test or training routine, the output forcesand/or moments determined using the force measurement assembly 102 maybe used to determine: (i) a quantitative score of the subject's swayduring the trials of the test or training routine (e.g., see sway anglecalculations described above), (ii) the type of strategy used by thesubject 108 to maintain his or her balance (e.g., hip or ankle strategy)during the trials of the test or training routine, (iii) the changes inthe center of gravity of the subject 108 during the trials of the testor training routine (e.g., refer to center of gravity determinationdescribed above), (iv) one or more quantitative sensory scoresindicative of which sensory system(s) are impaired (i.e., indicative ofwhether one or more of the somatosensory, vestibular and visual systemsare impaired), (v) the latency time of the subject 108 (e.g., the amountof time that it takes for the subject 108 to respond to a translationalor rotational perturbation of the force measurement assembly 102), (vi)the weight symmetry of the subject 108 (i.e., how much weight is beingplaced on the right leg versus the left leg), (vii) the amount of forcethat the subject 108 is able to exert in order to bring his or her bodyback to equilibrium after a perturbation (e.g., the amount of forceexerted by the subject 108 in response to a translational or rotationalperturbation of the force measurement assembly 102), and (viii) the swayenergy of the subject 108 in response to a perturbation (e.g., theanterior-posterior sway of the subject 108 in response to atranslational or rotational perturbation of the force measurementassembly 102).

In one or more embodiments, the head-mounted visual display device 344may have an organic light-emitting diode (OLED) display or liquidcrystal display (LCD) with a resolution of at least 2160 pixels in thehorizontal direction by 1200 pixels in the vertical direction (or 1080by 1200 pixel resolution for each eye of the subject). Also, in one ormore embodiments, the head-mounted visual display device 344 may have arefresh rate of at least 59 Hertz, or alternatively, at least 90 Hertz.In one or more further embodiments, the head-mounted visual displaydevice 344 may have a refresh rate between approximately 59 Hertz andapproximately 240 Hertz, inclusive (or between 59 Hertz and 240 Hertz,inclusive). Moreover, in one or more embodiments, the display latency ordisplay time lag of the head-mounted visual display device 344 (i.e.,amount of time that it takes for the pixels of the display to update inresponse to the head movement of the user) is between approximately 50milliseconds and approximately 70 milliseconds, inclusive (or between 50milliseconds and 70 milliseconds, inclusive). In one or more furtherembodiments, the head-mounted visual display device 344 may have adisplay latency or display time between approximately 10 millisecondsand approximately 50 milliseconds, inclusive (or between 10 millisecondsand 50 milliseconds, inclusive). Furthermore, in one or moreembodiments, the data acquisition/data processing device 104 that isoperatively coupled to the head-mounted visual display device 344 mayexecute a machine learning algorithm for predictive tracking of thesubject's head movement so as to predict how the subject is going tomove and pre-render the correct image for that view, therebysignificantly decreasing the display latency or display time lag.

Also, in one or more embodiments, the head-mounted visual display device344 may have a horizontal field of view of at least 50 degrees and avertical field of view of at least 50 degrees. More particularly, in oneor more further embodiments, the head-mounted visual display device 344may have a horizontal field of view of at least 110 degrees and avertical field of view of at least 90 degrees. In yet one or morefurther embodiments, the head-mounted visual display device 344 may havea horizontal field of view of at least 210 degrees and a vertical fieldof view of at least 130 degrees. In still one or more furtherembodiments, the head-mounted visual display device 344 may have ahorizontal field of view between approximately 100 degrees andapproximately 210 degrees, inclusive (or between 100 degrees and 210degrees, inclusive), and a vertical field of view between approximately60 degrees and approximately 130 degrees, inclusive (or between 60degrees and 130 degrees, inclusive). Advantageously, maximizing thehorizontal and vertical fields of view results in a more immersiveexperience for the subject because a greater portion of the subject'speripheral vision is covered.

In one or more embodiments, the head-mounted visual display device 344may be operatively coupled to the data acquisition/data processingdevice 104 by one or more wired connections. For example, the videosignal(s) for the head-mounted visual display device 344 may betransmitted using a high-definition multimedia interface (HDMI) cableand the data signal(s) for the head-mounted visual display device 344may be transmitted using a Universal Serial Bus (USB) cable. Thehead-mounted visual display device 344 may also include a wired powerconnection. In one or more alternative embodiments, the head-mountedvisual display device 344 may be operatively coupled to the dataacquisition/data processing device 104 using a wireless connectionrather than hardwired connection(s).

In one or more embodiments, in order to effectively handle the dataprocessing associated with the head-mounted visual display device 344,the data acquisition/data processing device 104 coupled to thehead-mounted visual display device 344 may have a high performancemicroprocessor, one or more high performance graphics cards, andsufficient random-access memory (RAM). For example, in an illustrativeembodiment, the data acquisition/data processing device 104 coupled tothe head-mounted visual display device 344 may have an Intel® Core i5processor or greater, one or more NVIDIA® GeForce 900 series graphicsprocessing units (GPU) or a higher series GPU, and eight (8) gigabytesof random-access memory (RAM) or greater.

In one or more embodiments, the head-mounted visual display device 344may incorporate an integral inertial measurement unit (IMU) with anaccelerometer, magnetometer, and gyroscope for sensing the head movementof the subject. Also, the head-mounted visual display device 344 mayinclude optical-based outside-in positional tracking for tracking theposition and orientation of the head-mounted visual display device 344in real time. The optical-based outside-in positional tracking mayinclude remote optical photosensors that detect infrared light-emittingdiode (LED) markers on the head-mounted visual display device 344, orconversely, remote infrared light-emitting diode (LED) beams that aredetected by photosensors on the head-mounted visual display device 344.

In one or more embodiments, the head-mounted visual display device 344may be formed using lightweight materials (e.g., lightweight polymericmaterials or plastics) so as to minimize the weight of the head-mountedvisual display device 344 on the subject.

Referring again to FIG. 53, it can be seen that the force measurementsystem illustrated therein may also be provided with a wall-mountedvisual display device 346 comprising a plurality of flat display screens348 arranged or joined together in a concave arrangement so as to atleast partially circumscribe the three sides of the torso of the subject108. As such, rather than using the head-mounted visual display device344, the scenes creating the simulated environment for the subject 108may be displayed on the plurality of flat display screens 348 in FIG.53. In an alternative embodiment, rather than using the plurality offlat display screens 348 arranged or joined together in the concavearrangement of FIG. 53, a continuously curved display screen may be usedto display the immersive scenes to the subject 108, the curved displayscreen engaging enough of the peripheral vision of the subject 108 suchthat the subject 108 becomes immersed in the simulated environment. Inanother alternative embodiment, rather than using the plurality of flatdisplay screens 348 arranged or joined together in the concavearrangement of FIG. 53 or a continuously curved display screen, awall-mounted flat display screen may be used to display the immersivescenes to the subject 108. While in the aforedescribed alternativeembodiments, these other visual display screens may be used with thebase assembly 106 and the displaceable force measurement assembly 102depicted in FIG. 53, it is to be understood that these otherwall-mounted visual displays do not have an immersive effect that isequivalent to the generally hemispherical projection screen 168described above because the subject 108 is not as encapsulated by thesealternative visual displays (i.e., these alternative visual displayslack the wraparound side portions and wraparound top and bottom portionsthat are provided by the generally hemispherical projection screen 168).

As described above in conjunction with the preceding embodiments, thedata acquisition/data processing device 104 of the force measurementsystem illustrated in FIG. 53 may further perturb the visual input ofthe subject 108 during the performance of the balance test or trainingroutine by manipulating the scenes on the output screen of the visualdisplay device. Also, in the embodiment of FIG. 53, and the otherembodiments described above, the force measurement system may furthercomprise an eye movement tracking device configured to track eyemovement and/or eye position of the subject 108 while the subject 108performs the balance test or training routine (e.g., the eye movementtracking device 312 described hereinafter in conjunction with FIG. 50).In this embodiment, the eye movement tracking device outputs one or moreeye tracking signals to the data acquisition/data processing device 104,and the data acquisition/data processing device 104 utilizes the eyetracking signals in order to assess a response of the subject 108 to theperturbed visual input (i.e., by measuring the eye movement of thesubject 108 in response to a displaced image on the output screen of thevisual display device). In one or more embodiments, the eye movementtracking device may be incorporated into the head-mounted visual displaydevice 344 depicted in FIG. 53.

In yet one or more alternative embodiments of the invention, a forcemeasurement assembly 102′ in the form of a static force plate, such asthat illustrated in FIG. 52, may be used with the head-mounted visualdisplay device 344, rather than the displaceable force measurementassembly 102 and base assembly 106 of FIG. 53. Similar to that describedabove in conjunction with the preceding embodiments, the dataacquisition/data processing device of the static force plate system mayperturb the visual input of the subject during the performance of thebalance test or training routine by manipulating the scenes on theoutput screen of the head-mounted visual display device 344. During theperformance of the balance test or training routine while the subject isdisposed on the static force plate, the data acquisition/data processingdevice may be further programmed to utilize the output forces and/ormoments computed from the output data of the static force plate in orderto assess a response of the subject to the visual stimuli on the outputscreen of the head-mounted visual display device 344. For example, toassess the response of the subject 108 during the performance of thebalance test or training routine, the output forces and/or momentsdetermined using the force measurement assembly 102 may be used todetermine any of the scores or parameters (i)-(viii) described above inconjunction with the embodiment illustrated in FIG. 53.

In one or more embodiments, the data acquisition/data processing device104 coupled to the head-mounted visual display device 344 is programmedto generate one or more scenes of a simulated and/or augmentedenvironment displayed on the head-mounted visual display device 344, andfurther generate one or more clinician screens (e.g., one or morescreens with test results) that are displayed on an additional visualdisplay device visible to a clinician (e.g., operator visual displaydevice 130 in FIG. 1). In these one or more embodiments, the one or morescenes of the simulated and/or augmented environment that are displayedon the head-mounted visual display device 344 comprise a plurality oftargets or markers (e.g., the plurality of targets or markers 238′ inFIG. 23) and at least one displaceable visual indicator (e.g., thedisplaceable visual indicator or cursor 240′ in FIG. 23), and the dataacquisition/data processing device 104 is programmed to control themovement of the at least one displaceable visual indicator 240′ towardsthe plurality of targets or markers 238′ based upon one or more computednumerical values (e.g., the center of pressure coordinates) determinedusing the output forces and/or moments of the force measurement assembly102.

In further embodiments of the invention, the data acquisition/dataprocessing device 104 is configured to control the movement of a gameelement of an interactive game displayed on the immersive subject visualdisplay device 107 by using one or more numerical values determined fromthe output signals of the force transducers associated with the forcemeasurement assembly 102. Referring to screen images 210, 210′, 218illustrated in FIGS. 16-21 and 27, it can be seen that the game elementmay comprise, for example, an airplane 214, 214′ that can be controlledin a virtual reality environment 212, 212′ or a skier 222 that iscontrolled in a virtual reality environment 220. With particularreference to FIG. 16, because a subject 204 is disposed within theconfines of the generally hemispherical projection screen 168 whileplaying the interactive game, he or she is completely immersed in thevirtual reality environment 212. FIG. 16 illustrates a first variationof this interactive game, whereas FIGS. 17-21 illustrate a secondvariation of this interactive game (e.g., each variation of the gameuses a different airplane 214, 214′ and different scenery). AlthoughFIGS. 17-21 depict generally planar images, rather than a concave imageprojected on a generally hemispherical screen 168 as shown in FIG. 16,it is to be understood that the second variation of the interactive game(FIGS. 17-21) is equally capable of being utilized on a screen that atleast partially surrounds a subject (e.g., a generally hemisphericalprojection screen 168). In the first variation of the interactiveairplane game illustrated in FIG. 16, arrows 211 can be provided inorder to guide the subject 204 towards a target in the game. Forexample, the subject 204 may be instructed to fly the airplane 214through one or more targets (e.g., rings or hoops) in the virtualreality environment 212. When the airplane is flown off course by thesubject 204, arrows 211 can be used to guide the subject 204 back to thegeneral vicinity of the one or more targets.

With reference to FIGS. 25 and 26, a target in the form of a ring orhoop 216 is illustrated in conjunction with the second variation of theinteractive airplane game. In this virtual reality scenario 212″, asubject is instructed to fly the airplane 214′ through the ring 216. InFIG. 25, the airplane 214′ is being displaced to the left by the subjectthrough the ring 216, whereas, in FIG. 26, the airplane 214′ is beingdisplaced to the right by the subject through the ring 216.Advantageously, the airplane simulation game is a type of training thatis more interactive for the patient. An interactive type of training,such as the airplane simulation game, improves patient compliance bymore effectively engaging the subject in the training. In addition, inorder to further increase patient compliance, and ensure that thesubject exerts his or her full effort, a leaderboard with scores may beutilized in the force measurement system 100. To help ensure subjectperformance comparisons that are fair to the participants, separateleaderboards may be utilized for different age brackets.

In some embodiments, the position of the rings or hoops 216 in thevirtual reality scenario 212″ could be selectively displaceable in aplurality of different positions by a user or operator of the system100. For example, the data acquisition/data processing device 104 couldbe specially programmed with a plurality of predetermined difficultylevels for the interactive airplane game. A novice difficulty levelcould be selected by the user or operator of the system 100 for asubject that requires a low level of difficulty. Upon selecting thenovice difficulty level, the rings or hoops 216 would be placed in theeasiest possible locations within the virtual reality scenario 212″. Fora subject requiring a higher level of difficulty, the user or operatorof the system 100 could select a moderate difficulty level, wherein therings or hoops 216 are placed in locations that are more challengingthan the locations used in the novice difficulty level. Finally, if asubject requires a maximum level of difficulty, the user or operatorcould select a high difficulty level, wherein the rings or hoops 216 areplaced in extremely challenging locations in the virtual realityscenario 212″. In addition, in some embodiments, the position of therings or hoops 216 in the virtual reality scenario 212″ could berandomly located by the data acquisition/data processing device 104 sothat a subject undergoing multiple training sessions using theinteractive airplane game would be unable to memorize the locations ofthe rings or hoops 216 in the scenario 212″, thereby helping to ensurethe continued effectiveness of the training.

In yet a further embodiment of the invention, the interactive type ofsubject or patient training may comprise an interactive skiing game. Forexample, as illustrated in the screen image 218 of FIG. 27, theimmersive virtual reality environment 220 may comprise a scenariowherein the subject controls a skier 222 on a downhill skiing course.Similar to the interactive airplane game described above, theinteractive skiing game may comprise a plurality of targets in the formsof gates 224 that the subject is instructed to contact while skiing thedownhill course. To make the interactive skiing game even more engagingfor the subject, a plurality of game performance parameters may belisted on the screen image, such as the total distance traveled 226(e.g., in meters), the skier's speed 228 (e.g., in kilometers per hour),and the skier's time 230 (e.g., in seconds).

In an illustrative embodiment, the one or more numerical valuesdetermined from the output signals of the force transducers associatedwith the force measurement assembly 102 comprise the center of pressurecoordinates (x_(P), y_(P)) computed from the ground reaction forcesexerted on the force plate assembly 102 by the subject. For example,with reference to the force plate coordinate axes 150, 152 of FIG. 7,when a subject leans to the left on the force measurement assembly 102′(i.e., when the x-coordinate x_(P) of the center of pressure ispositive), the airplane 214′ in the interactive airplane game isdisplaced to the left (see e.g., FIG. 18) or the skier 222 in theinteractive skiing game is displaced to the left (see e.g., FIG. 27).Conversely, when a subject leans to the right on the force measurementassembly 102′ (i.e., when the x-coordinate x_(P) of the center ofpressure is negative in FIG. 7), the airplane 214′ in the interactiveairplane game is displaced to the right (see e.g., FIG. 19) or the skier222 in the interactive skiing game is displaced to the right (see e.g.,FIG. 27). When a subject leans forward on the force measurement assembly102′ (i.e., when the y-coordinate y_(P) of the center of pressure ispositive in FIG. 7), the altitude of the airplane 214′ in theinteractive airplane game is increased (see e.g., FIG. 20) or the speedof the skier 222 in the interactive skiing game is increased (see e.g.,FIG. 27). Conversely, when a subject leans backward on the forcemeasurement assembly 102′ (i.e., when the y-coordinate y_(P) of thecenter of pressure is negative in FIG. 7), the altitude of the airplane214′ in the interactive airplane game is decreased (see e.g., FIG. 21)or the speed of the skier 222 in the interactive skiing game isdecreased (see e.g., FIG. 27).

In still a further embodiment, a force and motion measurement system isprovided that includes both the force measurement system 100 describedabove together with a motion detection system 300 that is configured todetect the motion of one or more body gestures of a subject (see FIGS.32 and 33). For example, during a particular training routine, a subjectmay be instructed to reach for different targets on the output screen168. While the subject reaches for the different targets on the outputscreen 168, the motion detection system 300 detects the motion of thesubject's body gestures (e.g., the motion detection system 300 tracksthe movement of one of the subject's arms while reaching for an objecton the output screen 168). As shown in FIG. 33, a subject 108 isprovided with a plurality of markers 304 disposed thereon. These markers304 are used to record the position of the limbs of the subject in3-dimensional space. A plurality of cameras 302 are disposed in front ofthe subject visual display device 107 (and behind the subject 108), andare used to track the position of the markers 304 as the subject moveshis or her limbs in 3-dimensional space. While three (3) cameras aredepicted in FIGS. 32 and 33, one of ordinary skill in the art willappreciate that more or less cameras can be utilized, provided that atleast two cameras 302 are used. In one embodiment of the invention, thesubject has a plurality of single markers applied to anatomicallandmarks (e.g., the iliac spines of the pelvis, the malleoli of theankle, and the condyles of the knee), or clusters of markers applied tothe middle of body segments. As the subject 108 executes particularmovements on the force measurement assembly 102, and within thehemispherical subject visual display device 107, the dataacquisition/data processing device 104 calculates the trajectory of eachmarker 304 in three (3) dimensions. Then, once the positional data isobtained using the motion detection system 300 (i.e., the motionacquisition/capture system 300), inverse kinematics can be employed inorder to determine the joint angles of the subject 108.

While the motion detection system 300 described above employs aplurality of markers 304, it is to be understood that the invention isnot so limited. Rather, in another embodiment of the invention, amarkerless motion detection/motion capture system is utilized. Themarkerless motion detection/motion capture system uses a plurality ofhigh speed video cameras to record the motion of a subject withoutrequiring any markers to be placed on the subject. Both of theaforementioned marker and markerless motion detection/motion capturesystems are optical-based systems. In one embodiment, the optical motiondetection/motion capture system 300 utilizes visible light, while inanother alternative embodiment, the optical motion detection/motioncapture system 300 employs infrared light (e.g., the system 300 couldutilize an infrared (IR) emitter to project a plurality of dots ontoobjects in a particular space as part of a markless motion capturesystem). For example, as shown in FIG. 50, a motion capture device 318with one or more cameras 320, one or more infrared (IR) depth sensors322, and one or more microphones 324 may be used to provide full-bodythree-dimensional (3D) motion capture, facial recognition, and voicerecognition capabilities. It is also to be understood that, rather thanusing an optical motion detection/capture system, a suitable magnetic orelectro-mechanical motion detection/capture system can also be employedin the system 100 described herein.

In some embodiments, the motion detection system 300, which is shown inFIGS. 32 and 33, is used to determine positional data (i.e.,three-dimensional coordinates) for one or more body gestures of thesubject 108 during the performance of a simulated task of daily living.The one or more body gestures of the subject 108 may comprise at leastone of: (i) one or more limb movements of the subject, (ii) one or moretorso movements of the subject, and (iii) a combination of one or morelimb movements and one or more torso movements of the subject 108. Inorder to simulate a task of daily living, one or more virtual realityscenes can be displayed on the subject visual display device 107. Onesuch exemplary virtual reality scene is illustrated in FIG. 37. Asillustrated in the screen image 244 of FIG. 37, the immersive virtualreality environment 246 simulating the task of daily living couldcomprise a scenario wherein a subject 204 is removing an object 248(e.g., a cereal box) from a kitchen cabinet 250. While the subject 204is performing this simulated task, the data acquisition/data processingdevice 104 could quantify the performance of the subject 204 during theexecution of the task (e.g., removing the cereal box 248 from thekitchen cabinet 250) by analyzing the motion of the subject's left arm252, as measured by the motion detection system 300. For example, byutilizing the positional data obtained using the motion detection system300, the data acquisition/data processing device 104 could compute thethree-dimensional (3-D) trajectory of the subject's left arm 252 throughspace. The computation of the 3-D trajectory of the subject's left arm252 is one exemplary means by which the data acquisition/data processingdevice 104 is able to quantify the performance of a subject during theexecution of a task of daily living. At the onset of the training for asubject 204, the 3-D trajectory of the subject's left arm 252 mayindicate that the subject 204 is taking an indirect path (i.e., a zigzagpath or jagged path 256 indicated using dashed lines) in reaching forthe cereal box 248 (e.g., the subject's previous injury may be impairinghis or her ability to reach for the cereal box 248 in the most efficientmanner). However, after the subject 204 has been undergoing training fora continuous period of time, the 3-D trajectory of the subject's leftarm 252 may indicate that the subject 204 is taking a more direct path(i.e., an approximately straight line path 254) in reaching for thecereal box 248 (e.g., the training may be improving the subject'sability to reach for the cereal box 248 in an efficient fashion). Assuch, based upon a comparison of the subject's left arm trajectorypaths, a physical therapist treating the subject or patient 204 mayconclude that the subject's condition is improving over time. Thus,advantageously, the motion detection system 300 enables a subject'smovement to be analyzed during a task of daily living so that adetermination can be made as to whether or not the subject's conditionis improving.

Moreover, in other embodiments, the motion detection system 300 may alsobe used to determine the forces and/or moments acting on the joints of asubject 108. In particular, FIG. 34 diagrammatically illustrates anexemplary calculation procedure 400 for the joint angles, velocities,and accelerations carried out by the force and motion measurement systemthat includes the motion detection system 300 depicted in FIGS. 32 and33. Initially, as shown in block 402 of FIG. 34, the plurality ofcameras 302 are calibrated using the image coordinates of calibrationmarkers and the three-dimensional (3-D) relationship of calibrationpoints such that a plurality of calibration parameters are generated. Inone exemplary embodiment of the invention, the calibration of theplurality of cameras 302 is performed using a Direct LinearTransformation (“DLT”) technique and yields eleven (11) DLT parameters.However, it is to be understood that, in other embodiments of theinvention, a different technique can be used to calibrate the pluralityof cameras 302. Then, in block 404, the perspective projection of theimage coordinates of the body markers 304 is performed using thecalibration parameters so that the image coordinates are transformedinto actual three-dimensional (3-D) coordinates of the body markers 304.Because the digitization of the marker images involves a certain amountof random error, a digital filter is preferably applied to thethree-dimensional (3-D) coordinates of the markers to remove theinherent noise in block 406. Although, it is to be understood that theuse of a digital filter is optional, and thus is omitted in someembodiments of the invention. In block 408, local coordinate systems areutilized to determine the orientation of the body segments relative toeach other. After which, in block 410, rotational parameters (e.g.,angles, axes, matrices, etc.) and the inverse kinematics model are usedto determine the joint angles. The inverse kinematics model contains thedetails of how the angles are defined, such as the underlyingassumptions that are made regarding the movement of the segmentsrelative to each other. For example, in the inverse kinematics model,the hip joint could be modeled as three separate revolute joints actingin the frontal, horizontal, and sagittal plane, respectively. In block412, differentiation is used to determine the joint velocities andaccelerations from the joint angles. Although, one of ordinary skill inthe art will appreciate that, in other embodiments of the invention,both differentiation and analytical curve fitting could be used todetermine the joint velocities and accelerations from the joint angles.

In addition, FIG. 34 diagrammatically illustrates the calculationprocedure for the joint forces and moments that is also carried out bythe force and motion measurement system, which comprises the forcemeasurement system 100 and motion detection system 300 of FIGS. 32-33.Referring again to this figure, antrophometric data is applied to asegment model in block 416 in order to determine the segment inertialparameters. By using the segment inertial parameters together with thejoint velocities and accelerations and the force plate measurements,joint and body segment kinetics are used in block 414 to determine thedesired joint forces and moments. In a preferred embodiment of theinvention, Newton-Euler Formulations are used to compute the jointforces and moments. However, it is to be understood that the inventionis not so limited. Rather, in other embodiments of the invention, thekinetics analysis could be carried out using a different series ofequations. In order to more clearly illustrate the requisitecalculations for determining the joint forces and moments, thedetermination of the joint reaction forces and joint moments of thesubject will be explained using an exemplary joint of the body.

In particular, the computation of the joint reaction forces and jointmoments of the subject will be described in reference to an exemplarydetermination of the forces and moments acting on the ankle. The forcemeasurement assembly 102 is used to determine the ground reaction forcesand moments associated with the subject being measured. These groundreaction forces and moments are used in conjunction with the jointangles computed from the inverse kinematics analysis in order todetermine the net joint reaction forces and net joint moments of thesubject. In particular, inverse dynamics is used to calculate the netjoint reaction forces and net joint moments of the subject by using thecomputed joint angles, angular velocities, and angular accelerations ofa musculoskeletal model, together with the ground reaction forces andmoments measured by the force measurement assembly 102.

An exemplary calculation of the forces and moments at the ankle jointwill be explained with reference to the foot diagram of FIG. 35 and thefree body diagram 500 depicted in FIG. 36. In FIGS. 35 and 36, the anklejoint 502 is diagrammatically represented by the point “A”, whereas thegravitational center 504 of the foot is diagrammatically represented bythe circular marker labeled “GF”. In this figure, the point ofapplication for the ground reaction forces {circumflex over (F)}_(Gr)(i.e., the center of pressure 506) is diagrammatically represented bythe point “P” in the free body diagram 500. The force balance equationand the moment balance equation for the ankle are as follows:m _(F) ·{right arrow over (a)} _(GF) ={right arrow over (F)} _(Gr)+{right arrow over (F)} _(A)  (4)J̆ _(F) {dot over (ω)} _(F)+{right arrow over (ω)}_(F) ×J̆ _(F){rightarrow over (ω)}_(F) ={right arrow over (M)} _(A) +{right arrow over(T)}+({right arrow over (r)} _(GA) ×{right arrow over (F)} _(A))+({rightarrow over (r)} _(GP) ×{right arrow over (F)} _(Gr))  (5)

where:

m_(F): mass of the foot

{right arrow over (a)}_(GF): acceleration of the gravitational center ofthe foot

{right arrow over (F)}_(Gr): ground reaction forces

{right arrow over (F)}_(A): forces acting on the ankle

J̆_(F): rotational inertia of the foot

{dot over (ω)} _(F): angular acceleration of the foot

{right arrow over (ω)}_(F): angular velocity of the foot

{right arrow over (M)}_(A): moments acting on the ankle

{right arrow over (T)}: torque acting on the foot

{right arrow over (r)}_(GA): position vector from the gravitationalcenter of the foot to the center of the ankle

{right arrow over (r)}_(GP): position vector from the gravitationalcenter of the foot to the center of pressure

In above equations (4) and (5), the ground reaction forces {circumflexover (F)}_(Gr) are equal in magnitude and opposite in direction to theexternally applied forces {right arrow over (F)}_(e) that the bodyexerts on the supporting surface through the foot (i.e., {right arrowover (F)}_(Gr)=−{right arrow over (F)}_(e)).

Then, in order to solve for the desired ankle forces and moments, theterms of equations (4) and (5) are rearranged as follows:{right arrow over (F)} _(A) =m _(F) ·{right arrow over (a)} _(GF)−{right arrow over (F)} _(Gr)  (6){right arrow over (M)} _(A) =J̆ _(F) {dot over (ω)} _(F)+{right arrowover (ω)}_(F) ×J̆ _(F){right arrow over (ω)}_(F) −{right arrow over(T)}−({right arrow over (r)} _(GA) ×{right arrow over (F)} _(A))−({rightarrow over (r)} _(GP) ×{right arrow over (F)} _(Gr))  (7)

By using the above equations, the magnitude and directions of the ankleforces and moments can be determined. The net joint reaction forces andmoments for the other joints in the body can be computed in a similarmanner.

In an alternative embodiment, the motion detection system that isprovided in conjunction with the force measurement system 100 maycomprise a plurality of inertial measurement units (IMUs), rather thantaking the form of a marker-based or markerless motion capture system.As described above for the motion detection system 300, the IMU-basedmotion detection system 300′ may be used to detect the motion of one ormore body gestures of a subject (see e.g., FIG. 49). As shown in FIG.49, a subject or patient 108 may be provided with a plurality ofinertial measurement units 306 disposed thereon. The one or more bodygestures of the subject 108 may comprise one or more limb movements ofthe subject, one or more torso movements of the subject, or acombination of one or more limb movements and one or more torsomovements of the subject.

As shown in FIG. 49, a subject or patient 108 may be outfitted with aplurality of different inertial measurement units 306 for detectingmotion. In the illustrative embodiment, the subject 108 is provided withtwo (2) inertial measurement units 306 on each of his legs 108 a, 108 b(e.g., on the side of his legs 108 a, 108 b). The subject is alsoprovided with two (2) inertial measurement units 306 on each of his arms108 c, 108 d (e.g., on the side of his arms 108 c, 108 d). In addition,the subject 108 of FIG. 49 is provided with an inertial measurement unit306 around his waist (e.g., with the IMU located on the back side of thesubject 108), and another inertial measurement unit 306 around his orher chest (e.g., with the IMU located on the front side of the subject108 near his sternum). In the illustrated embodiment, each of theinertial measurement units 306 is operatively coupled to the dataacquisition/data processing device 104 by wireless means, such asBluetooth, or another suitable type of personal area network wirelessmeans.

In the illustrated embodiment of FIG. 49, each of the inertialmeasurement units 306 is coupled to the respective body portion of thesubject 108 by a band 308. As shown in FIG. 49, each of the inertialmeasurement units 306 comprises an IMU housing 310 attached to anelastic band 308. The band 308 is resilient so that it is capable ofbeing stretched while being placed on the subject 108 (e.g., toaccommodate the hand or the foot of the subject 108 before it is fittedin place on the arm 108 c, 108 d or the leg 108 a, 108 b of the subject108). The band 308 can be formed from any suitable stretchable fabric,such as neoprene, spandex, and elastane. Alternatively, the band 308could be formed from a generally non-stretchable fabric, and be providedwith latching means or clasp means for allowing the band 308 to be splitinto two portions (e.g., the band 308 could be provided with a snap-typelatching device).

In other embodiments, it is possible to attach the inertial measurementunits 306 to the body portions of the subject 108 using other suitableattachment means. For example, the inertial measurement units 306 may beattached to a surface (e.g., the skin or clothing item of the subject108 using adhesive backing means. The adhesive backing means maycomprise a removable backing member that is removed just prior to theinertial measurement unit 306 being attached to a subject 108 or object.Also, in some embodiments, the adhesive backing means may comprise aform of double-sided bonding tape that is capable of securely attachingthe inertial measurement unit 306 to the subject 108 or another object.

In one or more embodiments, each inertial measurement unit 306 maycomprise a triaxial (three-axis) accelerometer sensing linearacceleration {right arrow over (a)}′, a triaxial (three-axis) rategyroscope sensing angular velocity {right arrow over (ω)}′, a triaxial(three-axis) magnetometer sensing the magnetic north vector {right arrowover (n)}′, and a central control unit or microprocessor operativelycoupled to each of accelerometer, gyroscope, and the magnetometer. Inaddition, each inertial measurement unit 306 may comprise a wirelessdata interface for electrically coupling the inertial measurement unit306 to the data acquisition/data processing device 104.

In one or more embodiments, the motion of the subject 108 may bedetected by the plurality of inertial measurement units 306 while one ormore images are displayed on the hemispherical projection screen 168 ofthe subject visual display device 107. The one or more images that aredisplayed on the screen 168 may comprise one or more simulated tasks,interactive games, training exercises, or balance tests. The dataacquisition/data processing device 104 is specially programmed toquantify the performance of a subject 108 during the execution of theone or more simulated tasks, interactive games, training exercises, orbalance tests by analyzing the motion of the one or more body gesturesof the subject 108 detected by the plurality of inertial measurementunits 306.

For example, as described above with regard to the motion detectionsystem 300, the inertial measurement units 306 of the motion detectionsystem 300′ may be used to determine positional data (i.e.,three-dimensional coordinates) for one or more body gestures of thesubject 108 during the performance of a simulated task of daily living.In order to simulate a task of daily living, one or more virtual realityscenes can be displayed on the subject visual display device 107. Onesuch exemplary virtual reality scene is illustrated in FIG. 50. Asillustrated in the screen image 244′ of FIG. 50, the immersive virtualreality environment 246′ simulating the task of daily living couldcomprise a scenario wherein a subject 204′ is pointing and/or grabbingtowards an object 248′ (e.g., a cereal box) that he is about ready tograsp from a kitchen cabinet 250′. While the subject 204′ is performingthis simulated task, the data acquisition/data processing device 104 mayquantify the performance of the subject 204′ during the execution of thetask (e.g., reaching for, and removing the cereal box 248′ from thekitchen cabinet 250′) by analyzing the motion of the subject's right arm251, as measured by the motion detection system 300′. For example, byutilizing the positional data obtained using the motion detection system300′ (with inertial measurement units (IMUs) 306), the dataacquisition/data processing device 104 may compute the three-dimensional(3-D) position and orientation of the subject's right arm 251 in space.The computation of the 3-D position and orientation of the subject'sright arm 251 is one exemplary means by which the data acquisition/dataprocessing device 104 is able to quantify the performance of a subjectduring the execution of a task of daily living. Thus, advantageously,the motion detection system 300′ enables a subject's movement to bequantified and analyzed during a task of daily living.

Next, an illustrative manner in which the data acquisition/dataprocessing device 104 of the force measurement system 100 performs theinertial measurement unit (IMU) calculations will be explained indetail. In particular, this calculation procedure will describe themanner in which the orientation and position of one or more bodyportions (e.g., limbs) of a subject 108, 204′ could be determined usingthe signals from the plurality of inertial measurement units (IMUs) 306of the motion detection system 300′. As explained above, in one or moreembodiments, each inertial measurement unit 306 includes the followingthree triaxial sensor devices: (i) a three-axis accelerometer sensinglinear acceleration {right arrow over (a)}′, (ii) a three-axis rategyroscope sensing angular velocity {right arrow over (ω)}′, and (iii) athree-axis magnetometer sensing the magnetic north vector {right arrowover (n)}′. Each inertial measurement unit 306 senses in the local(primed) frame of reference attached to the IMU itself. Because each ofthe sensor devices in each IMU is triaxial, the vectors {right arrowover (a)}′, {right arrow over (ω)}′, {right arrow over (n)}′ are each3-component vectors. A prime symbol is used in conjunction with each ofthese vectors to symbolize that the measurements are taken in accordancewith the local reference frame. The unprimed vectors that will bedescribed hereinafter are in the global reference frame.

The objective of these calculations is to find the orientation {rightarrow over (θ)}(t) and position {right arrow over (R)}(t) in the global,unprimed, inertial frame of reference. Initially, the calculationprocedure begins with a known initial orientation {right arrow over(θ)}₀ and position {right arrow over (R)}₀ in the global frame ofreference.

For the purposes of the calculation procedure, a right-handed coordinatesystem is assumed for both global and local frames of reference. Theglobal frame of reference is attached to the Earth. The acceleration dueto gravity is assumed to be a constant vector {right arrow over (g)}.Also, for the purposes of the calculations presented herein, it ispresumed the sensor devices of the inertial measurement units (IMUs)provide calibrated data. In addition, all of the signals from the IMUsare treated as continuous functions of time. Although, it is to beunderstood the general form of the equations described herein may bereadily discretized to account for IMU sensor devices that take discretetime samples from a bandwidth-limited continuous signal.

The orientation {right arrow over (θ)}(t) is obtained by singleintegration of the angular velocity as follows:

$\begin{matrix}{{\overset{\rightarrow}{\theta}(t)} = {{\overset{\rightarrow}{\theta}}_{0} + {\int_{0}^{t}{{\overset{\rightarrow}{\overset{\_}{\omega}}(t)}{dt}}}}} & (8) \\{{\overset{\rightarrow}{\theta}(t)} = {{\overset{\rightarrow}{\theta}}_{0} + {\int_{0}^{t}{{\overset{\rightarrow}{\Theta}(t)}{{\overset{\rightarrow}{\overset{\_}{\omega}}}^{\prime}(t)}{dt}}}}} & (9)\end{matrix}$where {right arrow over (Θ)}(t) is the matrix of the rotationtransformation that rotates the instantaneous local frame of referenceinto the global frame of reference.

The position is obtained by double integration of the linearacceleration in the global reference frame. The triaxial accelerometerof each IMU senses the acceleration {right arrow over (a)}′ in the localreference frame. The acceleration {right arrow over (a)}′ has thefollowing contributors: (i) the acceleration due to translationalmotion, (ii) the acceleration of gravity, and (iii) the centrifugal,Coriolis and Euler acceleration due to rotational motion. All but thefirst contributor has to be removed as a part of the change of referenceframes. The centrifugal and Euler accelerations are zero when theacceleration measurements are taken at the origin of the local referenceframe. The first integration gives the linear velocity as follows:

$\begin{matrix}{{\overset{\rightarrow}{v}(t)} = {{\overset{\rightarrow}{v}}_{0} + {\int_{0}^{t}{\left\{ \;{{\overset{\rightarrow}{a}(t)} - \overset{\rightarrow}{g}} \right\}{dt}}}}} & (10) \\{{\overset{\rightarrow}{v}(t)} = {{\overset{\rightarrow}{v}}_{0} + {\int_{0}^{t}{\left\{ {{{\overset{\rightarrow}{\Theta}(t)}\left\lbrack \;{{{\overset{\rightarrow}{a}}^{\prime}(t)} + {2\overset{\rightarrow}{\omega} \times {{\overset{\rightarrow}{v}}^{\prime}(t)}}} \right\rbrack} - \overset{\rightarrow}{g}} \right\}{dt}}}}} & (11)\end{matrix}$where 2{right arrow over (ω)}′×{right arrow over (v)}′(t) is theCoriolis term, and where the local linear velocity is given by thefollowing equation:{right arrow over (v)}′(t)={right arrow over (Θ)}⁻¹(t){right arrow over(v)}(t)  (12)The initial velocity {right arrow over (v)}₀ can be taken to be zero ifthe motion is being measured for short periods of time in relation tothe duration of Earth's rotation. The second integration gives theposition as follows:

$\begin{matrix}{{\overset{\rightarrow}{R}(t)} = {{\overset{\rightarrow}{R}}_{0} + {\int_{0}^{t}{{\overset{\rightarrow}{v}(t)}dt}}}} & (13)\end{matrix}$At the initial position, the IMU's local-to-global rotation's matrix hasan initial value {right arrow over (Θ)}(0)≡{right arrow over (Θ)}₀. Thisvalue can be derived by knowing the local and global values of both themagnetic north vector and the acceleration of gravity. Those two vectorsare usually non-parallel. This is the requirement for the {right arrowover (Θ)}₀({right arrow over (g)}′, {right arrow over (n)}′, {rightarrow over (g)}, {right arrow over (n)}) to be unique. The knowledge ofeither of those vectors in isolation gives a family of non-uniquesolutions {right arrow over (Θ)}₀({right arrow over (g)}′, {right arrowover (g)}) or {right arrow over (Θ)}₀({right arrow over (n)}′, {rightarrow over (n)}) that are unconstrained in one component of rotation.The {right arrow over (Θ)}₀({right arrow over (g)}′, {right arrow over(n)}′, {right arrow over (g)}, {right arrow over (n)}) has manyimplementations, with the common one being the Kabsch algorithm. Assuch, using the calculation procedure described above, the dataacquisition/data processing device 104 of the force measurement system100 may determine the orientation {right arrow over (θ)}(t) and position{right arrow over (R)}(t) of one or more body portions of the subject108, 204′. For example, the orientation of a limb of the subject 108,204′ (e.g., the right arm 251 of the subject 204′ in FIG. 50) may bedetermined by computing the orientation {right arrow over (θ)}(t) andposition {right arrow over (R)}(t) of two points on the limb of thesubject 108, 204′ (i.e., at the respective locations of two inertialmeasurement units (IMUs) 306 disposed on the limb of the subject 108,204′).

Referring again to FIG. 50, it can be seen that the subject 204′ is alsoprovided with an eye movement tracking device 312 that is configured totrack the eye movement and/or eye position of the subject 204′ (i.e.,the eye movement, the eye position, or the eye movement and the eyeposition of the subject 204′) while he performs the one or moresimulated tasks, interactive games, training exercises, or balancetests. The eye movement tracking device 312 may be utilized inconjunction with the motion detection system 300′. For example, in thevirtual reality environment 246′ of FIG. 50, the eye movement trackingdevice 312 may be used to determine the eye movement and/or eye positionof the subject 204′ while he performs the one or more simulated tasks,interactive games, training exercises, or balance tests. The eyemovement tracking device 312 may be in the form of the eye movementtracking devices described in U.S. Pat. Nos. 6,113,237 and 6,152,564,the entire disclosures of which are incorporated herein by reference.The eye movement tracking device 312 is configured to output one or morefirst signals that are representative of the detected eye movementand/or eye position of the subject 204′ (e.g., the saccadic eye movementof the subject). As explained above, the eye movement tracking device312 may be operatively connected to the input/output (I/O) module of theprogrammable logic controller 172, which in turn, is operativelyconnected to the data acquisition/data processing device 104. As will bedescribed in more detail hereinafter, referring again to FIG. 50, a headposition detection device (i.e., an inertial measurement unit 306) mayalso be provided on the head of the subject 204′ so that a head positionof the subject 204′ is capable of being determined together with the eyemovement and/or eye position of the subject 204′ determined using theeye movement tracking device 312. The head position detection device 306is configured to output one or more second signals that arerepresentative of the detected position of the head of the subject 204′.As such, using the one or more first output signals from the eyemovement tracking device 312 and the one or more second output signalsfrom head position detection device 306, the data acquisition/dataprocessing device 104 may be specially programmed to determine one ormore gaze directions of the subject 204′ (as diagrammatically indicatedby dashed line 342 in FIG. 50) during the performance of the one or moresimulated tasks, interactive games, training exercises, or balancetests. In addition, as will be described in further detail hereinafter,the data acquisition/data processing device 104 may be furtherconfigured to compare the one or more gaze directions of the subject204′ to the position of one or more objects (e.g., cereal box 248′) inthe one or more scene images of the at least one visual display deviceso as to determine whether or not the eyes of the subject 204′ areproperly directed at the object 248′ (e.g., cereal box) that is about tobe grasped by the subject 204′.

In one or more embodiments, the data acquisition/data processing device104 determines the one or more gaze directions of the subject 204′ as afunction of the eye angular position (θ_(E)) of the subject 204′determined by the eye movement tracking device 312 and the angularposition of the subject's head (θ_(H)) determined by the head positiondetection device 306. More particularly, in one or more embodiments, thedata acquisition/data processing device 104 is specially programmed todetermine the one or more gaze directions of the subject 204′ bycomputing the algebraic sum of the eye angular position (θ_(E)) of thesubject 204′ (as determined by the eye movement tracking device 312) andthe angular position (θ_(H)) of the subject's head (as determined by thehead position detection device 306).

In addition, the data acquisition/data processing device 104 may bespecially programmed to determine a position of one or more objects(e.g., the cereal box 248′ in FIG. 50) in the one or more scene images244′ of the visual display device. Once the position of the one or moreobjects on the screen of the visual display device are determined, thedata acquisition/data processing device 104 may be further speciallyprogrammed to compare the one or more gaze directions of the subject204′ (as detected from the output of the eye movement tracking device312 and head position detection device 306) to the position of one ormore objects on the screen of visual display device (e.g., by using aray casting technique to project the imaginary sight line 342 in FIG. 50determined from the output of the eye movement tracking device 312 andhead position detection device 306) towards one or more objects (e.g.,the cereal box 248′) in a virtual world. That is, one or more objects(e.g., the cereal box 248′) displayed on the visual display device maybe mapped into the virtual environment so that an intersection orcollision between the projected sight line 342 and the one or moreobjects may be determined. Alternatively, or in addition to, comparingthe one or more gaze directions of the subject to the position of one ormore objects on the screen, the data acquisition/data processing device104 may be specially programmed to compute a time delay between amovement of the one or more objects (e.g., the cereal box 248′) in theone or more scene images of the visual display device and a change inthe gaze direction of the subject 204′. For example, the dataacquisition/data processing device 104 may be specially programmed tomove or displace the object across the screen, then subsequentlydetermine how much time elapses (e.g., in seconds) before the subjectchanges his or her gaze direction in response to the movement of theobject. In an exemplary scenario, a clinician may instruct a patient tocontinually direct his or her eyes at a particular object on the screen.When the object is displaced on the screen, the time delay (or reactiontime of the subject) would be a measure of how long it takes the subjectto change the direction of his or her eyes in response to the movementof the object on the screen (i.e., so the subject is still staring atthat particular object).

When utilizing the eye movement tracking device 312, the dataacquisition/data processing device 104 may be specially programmed toassess a performance of the subject 204′ while performing one or moresimulated tasks, interactive games, training exercises, or balance testsusing the comparison of the one or more gaze directions of the subject204′ to the position of one or more objects or the computed time delayof the subject 204′. For example, if the comparison between the one ormore gaze directions of the subject 204′ to the position of one or moreobjects reveals that there is a large distance (e.g., 10 inches or more)between the projected sight line 342 of the subject's gaze direction andthe position determined for the one or more objects on the screen of thevisual display device, then the data acquisition/data processing device104 may determine that the performance of the subject 204′ during theone or more simulated tasks, interactive games, training exercises, orbalance tests is below a baseline normative value (i.e., below averageperformance). Conversely, if the comparison between the one or more gazedirections of the subject 204′ to the position of one or more objectsreveals that there is a small distance (e.g., 3 inches or less) betweenthe projected sight line 342 of the subject's gaze direction and theposition determined for the one or more objects on the screen of thevisual display device, then the data acquisition/data processing device104 may determine that the performance of the subject 204′ during theone or more simulated tasks, interactive games, training exercises, orbalance tests is above a baseline normative value (i.e., above averageperformance). Similarly, if the computed time delay between a movementof the one or more objects on the screen of the visual display deviceand a change in the subject's gaze direction is large (e.g., a largetime delay of 1 second or more), then the data acquisition/dataprocessing device 104 may determine that the performance of the subject204′ during the one or more simulated tasks, interactive games, trainingexercises, or balance tests is below a baseline normative value (i.e.,below average performance). Conversely, if the computed time delaybetween a movement of the one or more objects on the screen of thevisual display device and a change in the subject's gaze direction issmall (e.g., a small time delay of 0.25 seconds or less), then the dataacquisition/data processing device 104 may determine that theperformance of the subject 204′ during the one or more simulated tasks,interactive games, training exercises, or balance tests is above abaseline normative value (i.e., above average performance).

Also, as illustrated in FIG. 50, the subject 204′ is provided with ascene camera 314 mounted to the eye movement tracking device 312 so thatone or more video images of an environment surrounding the subject maybe captured, as the one or more gaze directions of the subject 204′ aredetermined using the output of the eye movement tracking device 312 andhead position detection device 306. The scene camera 314 records theenvironment surrounding the subject 204′ in relation to a video beingcaptured by a forward facing head-mounted camera. Similar to the eyemovement tracking device 312, the scene camera 314 may be operativelyconnected to the input/output (I/O) module of the programmable logiccontroller 172, which in turn, is operatively connected to the dataacquisition/data processing device 104. As such, using the one or moreoutput signals from the scene camera 314, the data acquisition/dataprocessing device 104 may be specially programmed to utilize the one ormore video images captured by the scene camera in a virtual realityenvironment 246′ displayed on the visual display device 107 during theperformance of the one or more simulated tasks, interactive games,training exercises, or balance tests. For example, in one or moreembodiments, the scene camera 314 may be used to add to the imagery in avirtual reality environment in which the subject 204′ is immersed. Inone or more alternative embodiments, the scene camera 314 may be used tocapture the gaze position of the subject 204′ while he or she interactsin a virtual reality environment (e.g., the virtual reality environment246′ in FIG. 50).

Turning once again to FIG. 50, it can be seen that the head positiondetection device (i.e., the inertial measurement unit 306) is disposedon the head of the subject 204′ so that a head position and orientationof the subject 204′ is capable of being determined together with the eyemovement and/or eye position of the subject 204′ determined using theeye movement tracking device 312, and the one or more video images of anenvironment surrounding the subject 204′ determined using the scenecamera 314. As such, using the one or more output signals from thehead-mounted inertial measurement unit 306, the data acquisition/dataprocessing device 104 may be specially programmed to calculate the headposition and orientation of the subject 204′ during the performance ofthe one or more simulated tasks, interactive games, training exercises,or balance tests (i.e., by using the calculation procedure describedabove for the IMUs 306). For example, in the virtual reality environment246′ of FIG. 50, the head-mounted inertial measurement unit 306 may beused to determine whether or not the head of the subject 204′ isproperly pointing toward the object 248′ (e.g., cereal box) that isabout to be grasped by the subject 204′.

In addition, as shown in FIG. 50, the subject 204′ may also be providedwith an instrumented motion capture glove 316 on his right hand in orderto detect one or more finger motions of the subject while the subjectperforms the one or more simulated tasks, interactive games, trainingexercises, or balance tests. The instrumented motion capture glove 316may comprise a plurality of different sensor devices, which may includea plurality of finger flexion or bend sensors on each finger, aplurality of abduction sensors, one or more palm-arch sensors, one ormore sensors measuring thumb crossover, one or more wrist flexionsensors, and one or more wrist abduction sensors. The sensor devices ofthe instrumented motion capture glove 316 may be attached to an elasticmaterial that fits over the hand of the subject 204′, which permits thesubject 204′ to manipulate his hand without any substantial decrease inmobility due the instrumented glove 316. The instrumented motion captureglove 316 outputs a plurality of signals that are representative of thedetected finger movement of the subject 204′. The instrumented motioncapture glove 316 may be operatively connected to the dataacquisition/data processing device 104 of the force measurement system100. The data acquisition/data processing device 104 may be speciallyprogrammed to determine the finger positions and orientations of thesubject during the performance of the one or more simulated tasks,interactive games, training exercises, or balance tests using theplurality of signals outputted by the instrumented motion capture glove316 (e.g., by executing calculations similar to those described abovefor the IMUs). In the illustrated embodiment, the instrumented motioncapture glove 316 is operatively connected to the data acquisition/dataprocessing device 104 by wireless means, such as Bluetooth, or anothersuitable type of personal area network wireless means.

In a further embodiment, a measurement and analysis system is providedthat generally includes a visual display device together with an eyemovement tracking device 312 and a data acquisition/data processingdevice 104. The eye movement tracking device 312 functions in the samemanner described above with regard to the preceding embodiments. Inaddition, the measurement and analysis system may also comprise thescene camera 314 and the head-mounted inertial measurement unit 306explained above.

In yet a further embodiment, a measurement and analysis system isprovided that generally includes a visual display device having anoutput screen, the visual display device configured to display one ormore scene images on the output screen so that the images are viewableby a subject; an object position detection system, the object positiondetection system configured to detect a position of a body portion of asubject 108, 204′ and output one or more first signals representative ofthe detected position; and a data acquisition/data processing device 104operatively coupled to the visual display device and the object positiondetection system. In this further embodiment, the object positiondetection system may comprise one or more of the following: (i) one ormore inertial measurement units 306 (e.g., see FIGS. 49 and 50), (ii) atouchscreen interface of the visual display device 130 (e.g., see FIG.1), (iii) one or more infrared (IR) sensing devices 322 (e.g., see FIG.50), and (iv) one or more cameras (e.g., see FIGS. 32 and 33).

In this further embodiment, the data acquisition/data processing device104 is specially programmed to receive the one or more first signalsthat are representative of the position of the body portion (e.g., anarm) of the subject 108, 204′ and to compute the position, orientation,or both the position and orientation, of the body portion (e.g., thearm) of the subject 108, 204′ using the one or more first signals. Forexample, the data acquisition/data processing device 104 may bespecially programmed to determine the position and orientation of an arm251 of the subject 108, 204′ using the output signals from a pluralityof inertial measurement units 306 attached along the length of thesubject's arm (e.g., as illustrated in FIG. 50). As explained above, thepositional coordinates of the subject's arm may be initially determinedrelative to a local coordinate system, and then subsequently transformedto a global coordinate system. In addition, the data acquisition/dataprocessing device 104 may be specially programmed to determine aposition of one or more objects (e.g., the cereal box 248′ in FIG. 50)in the one or more scene images 244′ of the visual display device. Forexample, the pixel coordinates (x pixels by y pixels) defining theposition of the object (e.g., the cereal box 248′) on the screen may betransformed into dimensional coordinates (e.g., x inches by y inches)using the physical size of the screen (e.g., 40 inches by 30 inches). Assuch, the position of the object (e.g., the cereal box 248′) on thescreen may be defined in terms of a global coordinate system having anorigin at the center of the visual display device. Also, the positionalcoordinates of the subject's arm may be transformed such that they arealso defined in accordance with the same global coordinate system havingits origin at the center of the visual display device.

Once the position and/or orientation of the body portion (e.g., the arm)of the subject 108, 204′ and the position of the one or more objects onthe screen of the visual display device are defined relative to the samecoordinate system, the data acquisition/data processing device 104 maybe further specially programmed to compute a difference value betweenthe computed position and/or orientation of the body portion (e.g., thearm) of the subject and the position determined for the one or moreobjects on the screen of the visual display device. For example, thedata acquisition/data processing device 104 may compute a distance valuebetween the coordinates of the arm of the subject and the coordinates ofthe one or more objects on the screen in order to assess how close thesubject's arm is to the intended object (e.g., the cereal box 248′) onthe screen (e.g., to determine if he or she is pointing at, or reachingfor, the correct object on the screen). Alternatively, or in additionto, computing the difference value, the data acquisition/data processingdevice 104 may be specially programmed to compute a time delay between amovement of the one or more objects on the screen of the visual displaydevice and a movement of the body portion (e.g., an arm) of the subject.For example, the data acquisition/data processing device 104 may bespecially programmed to move or displace the object across the screen,then subsequently determine how much time elapses (e.g., in seconds)before the subject moves his or her arm in response to the movement ofthe object. In an exemplary scenario, a clinician may instruct a patientto continually point to a particular object on the screen. When theobject is displaced on the screen, the time delay (or reaction time ofthe subject) would be a measure of how long it takes the subject to movehis or her arm in response to the movement of the object on the screen(i.e., so the subject is still pointing at that particular object).

In this further embodiment, the data acquisition/data processing device104 may be specially programmed to utilize a ray casting technique inorder to project an imaginary arm vector of the subject 204′, theorientation and position of which may be determined using the outputsignal(s) from one or more inertial measurement units 306 on the arm ofthe subject 204′ (see FIG. 50), towards one or more objects (e.g., thecereal box 248′) in a virtual world. That is, one or more objects (e.g.,the cereal box 248′) displayed on the visual display device may bemapped into the virtual environment so that an intersection or collisionbetween the projected arm vector and the one or more objects may bedetermined. As such, in one exemplary scenario, the dataacquisition/data processing device 104 is capable of determining whetheror not a subject 204′ is correctly pointing his or her arm in thedirection of a particular object (e.g., cereal box 248′) on the screenof the visual display device.

Also, in this further embodiment, the data acquisition/data processingdevice 104 may be specially programmed to assess a performance of thesubject 204′ while performing one or more simulated tasks, interactivegames, training exercises, or balance tests using the computeddifference value or the computed time delay of the subject 204′. Forexample, if the computed difference value between the calculatedposition and/or orientation of the body portion (e.g., the arm) of thesubject and the position determined for the one or more objects on thescreen of the visual display device is large (i.e., a large distance of20 inches or more), then the data acquisition/data processing device 104may determine that the performance of the subject 204′ during the one ormore simulated tasks, interactive games, training exercises, or balancetests is below a baseline normative value (i.e., below averageperformance). Conversely, if the computed difference value between thecalculated position and/or orientation of the body portion (e.g., thearm) of the subject and the position determined for the one or moreobjects on the screen of the visual display device is small (i.e., asmall distance of 3 inches or less), then the data acquisition/dataprocessing device 104 may determine that the performance of the subject204′ during the one or more simulated tasks, interactive games, trainingexercises, or balance tests is above a baseline normative value (i.e.,above average performance). Similarly, if the computed time delaybetween a movement of the one or more objects on the screen of thevisual display device and a movement of the body portion (e.g., an arm)of the subject is large (i.e., a large time delay of 1 second or more),then the data acquisition/data processing device 104 may determine thatthe performance of the subject 204′ during the one or more simulatedtasks, interactive games, training exercises, or balance tests is belowa baseline normative value (i.e., below average performance).Conversely, if the computed time delay between a movement of the one ormore objects on the screen of the visual display device and a movementof the body portion (e.g., an arm) of the subject is small (i.e., asmall time delay of 0.2 seconds or less), then the data acquisition/dataprocessing device 104 may determine that the performance of the subject204′ during the one or more simulated tasks, interactive games, trainingexercises, or balance tests is above a baseline normative value (i.e.,above average performance).

Also, in one or more other embodiments, the measurement and analysissystem described above may further comprise a force measurement assembly(e.g., force measurement assembly 102) configured to receive a subject.In addition, in one or more other embodiments, the measurement andanalysis system may additionally include the instrumented motion captureglove described in detail above.

In yet a further embodiment, a modified version of the force measurementsystem 100′ may comprise a force measurement device 600 in the form ofan instrumented treadmill. Like the force measurement assemblies 102,102′ described above, the instrumented treadmill 600 is configured toreceive a subject thereon. Refer to FIG. 38, it can be seen that thesubject visual display device 107′ is similar to that described above,except that the screen 168′ of the subject visual display device 107′ issubstantially larger than the screen 168 utilized in conjunction withthe force measurement system 100 (e.g., the diameter of the screen 168′is approximately two (2) times larger that of the screen 168). In oneexemplary embodiment, the projection screen 168′ has a width W_(S)′lying in the range between approximately one-hundred and eighty (180)inches and approximately two-hundred and forty (240) inches (or betweenone-hundred and eighty (180) inches and two-hundred and forty (240)inches). Also, rather than being supported on a floor surface using thescreen support structure 167 explained above, the larger hemisphericalscreen 168′ of FIG. 38 rests directly on the floor surface. Inparticular, the peripheral edge of the semi-circular cutout 178′, whichis located at the bottom of the screen 168′, rests directly on thefloor. The hemispherical screen 168′ of FIG. 38 circumscribes theinstrumented treadmill 600. Because the other details of the subjectvisual display device 107′ and the data acquisition/data processingdevice 104 are the same as that described above with regard to theaforementioned embodiments, no further description of these components104, 107′ will be provided for this embodiment.

As illustrated in FIG. 38, the instrumented treadmill 600 is attached tothe top of a motion base 602. The treadmill 600 has a plurality of topsurfaces (i.e., a left and right rotating belt 604, 606) that are eachconfigured to receive a portion of a body of a subject (e.g., the leftbelt of the instrumented treadmill 600 receives a left leg 108 a of asubject 108, whereas the right belt 606 of the instrumented treadmill600 receives a right leg 108 b of the subject 108). In a preferredembodiment, a subject 108 walks or runs in an upright position atop thetreadmill 600 with the feet of the subject contacting the top surfacesof the treadmill belts 604, 606. The belts 604, 606 of the treadmill 600are rotated by one or more electric actuator assemblies 608, whichgenerally comprise one or more electric motors. Similar to the forcemeasurement assemblies 102, 102′ described above, the instrumentedtreadmill 600 is operatively connected to the data acquisition/dataprocessing device 104 by an electrical cable. While it is not readilyvisible in FIG. 38 due to its location, the force measurement assembly610, like the force measurement assemblies 102, 102′, includes aplurality of force transducers (e.g., four (4) pylon-type forcetransducers) disposed below each rotating belt 604, 606 of the treadmill600 so that the loads being applied to the top surfaces of the belts604, 606 can be measured. Similar to that described above for the forcemeasurement assembly 102, the separated belts 604, 606 of theinstrumented treadmill 600 enables the forces and/or moments applied bythe left and right legs 108 a, 108 b of the subject 108 to beindependently determined. The arrows T1, T2, T3 disposed adjacent to themotion base 602 in FIG. 38 schematically depict the displaceable nature(i.e., the translatable nature) of the instrumented treadmill 600, whichis effectuated by the motion base 602, whereas the curved arrows R1, R2,R3 in FIG. 38 schematically illustrate the ability of the instrumentedtreadmill 600 to be rotated about a plurality of different axes, therotational movement of the instrumented treadmill 600 being generated bythe motion base 602.

The primary components of the motion base 602 are schematically depictedin FIGS. 39A and 39B. As depicted in these figures, the motion base 602comprises a movable top surface 612 that is preferably displaceable(i.e., translatable, as represented by straight arrows) and rotatable(as illustrated by curved arrows R1, R2) in 3-dimensional space by meansof a plurality of actuators 614. In other words, the motion base 602 ispreferably a six (6) degree-of-freedom motion base. The instrumentedtreadmill 600 is disposed on the movable top surface 612. The motionbase 602 is used for the dynamic testing of subjects when, for example,the subject is being tested, or is undergoing training, in a virtualreality environment. While the motion base 602 is preferablytranslatable and rotatable in 3-dimensional space, it is to beunderstood that the present invention is not so limited. Rather, motionbases 602 that only are capable of 1 or 2 dimensional motion could beprovided without departing from the spirit and the scope of the claimedinvention. Also, motion bases 602 that are only capable of either linearmotion or rotational motion are encompassed by the present invention.

Another modified version of the force measurement system 100″, whichcomprises a force measurement device 600′ in the form of an instrumentedtreadmill, is illustrated in FIG. 45. Similar to the instrumentedtreadmill in FIG. 38, the instrumented treadmill of FIG. 45 comprisesleft and right rotating belts 604, 606 and a force measurement assembly610 disposed underneath the treadmill belts 604, 606. The forcemeasurement system 100″ of FIG. 45 is similar in many respects to theforce measurement system 100′ of FIG. 38, except that the projectorarrangement is different from that of the FIG. 38 embodiment. Inparticular, in the embodiment of FIG. 45, two (2) projectors 164″, eachhaving a respective fisheye-type lens 182, are used to project an imageonto the generally hemispherical projection screen 168″. As illustratedin FIG. 45, each of the projectors 164″ generally rests on the topsurface of the floor, and has a fisheye-type lens 182 that is angledupward at an approximately 90 degree angle. Similar to that describedabove with regard to FIGS. 30 and 31, the projectors 164″ with thefisheye-type lenses 182 project intersecting light beams onto thegenerally hemispherical projection screen 168″. Advantageously, the useof two projectors 164″ with fisheye-type lenses 182, rather than just asingle projector 164″ with a fisheye lens 182, accommodates the largerdiameter projection screen 168″ that is utilized with the instrumentedtreadmill 600′, and it also has the added benefit of removing shadowsthat are cast on the output screen 168″ by the subject 108 disposed onthe force measurement assembly 600′.

In still a further embodiment of the invention, the virtual realityenvironment described herein may include the projection of an avatarimage onto the hemispherical projection screen 168 of the subject visualdisplay device 107. For example, as illustrated in the screen image 266of FIG. 40, the immersive virtual reality environment 268 may comprise ascenario wherein an avatar 270 is shown walking along a bridge 207. Theavatar image 270 on the screen 168 represents and is manipulated by thesubject 108 disposed on the force measurement assembly 102 or theinstrumented treadmill 600. The animated movement of the avatar image270 on the screen 168 is controlled based upon the positionalinformation acquired by the motion acquisition/capture system 300described above, as well as the force and/or moment data acquired fromthe force measurement assembly 102 or the instrumented treadmill 600. Inother words, an animated skeletal model of the subject 108 is generatedby the data acquisition/data processing device 104 using the acquireddata from the motion capture system 300 and the force measurementassembly 102 or the instrumented treadmill 600. The dataacquisition/data processing device 104 then uses the animated skeletalmodel of the subject 108 to control the movement of the avatar image 270on the screen 168.

The avatar image 270 illustrated in the exemplary virtual realityscenario of FIG. 40 has a gait disorder. In particular, it can be seenthat the left foot 272 of the avatar 270 is positioned in an abnormalmanner, which is indicative of the subject 108 who is controlling theavatar 270 having a similar disorder. In order to bring this gaitabnormality to the attention of the subject 108 and the clinicianconducting the evaluation and/or training of the subject, the left foot272 of the avatar 270 is shown in a different color on the screen 168(e.g., the left foot turns “red” in the image in order to clearlyindicate the gait abnormality). In FIG. 40, because this is ablack-and-white image, the different color (e.g., red) of the left foot272 of the avatar 270 is indicated using a hatching pattern (i.e., theavatar's left foot 272 is denoted using crisscross type hatching). It isto be understood that, rather than changing the color of the left foot272, the gait abnormality may indicated using other suitable means inthe virtual reality environment 268. For example, a circle could bedrawn around the avatar's foot 272 to indicate a gait disorder. Inaddition, a dashed image of an avatar having normal gait could bedisplayed on the screen 168 together with the avatar 270 so that thesubject 108 and the clinician could readily ascertain the irregularitiespresent in the subject's gait, as compared to a virtual subject withnormal gait.

In FIG. 41, another virtual reality environment utilizing an avatar 270′is illustrated. This figure is similar in some respects to FIG. 37described above, except that the avatar 270′ is incorporated into thevirtual reality scenario. As shown in the screen image 244′ of FIG. 41,the immersive virtual reality environment 246′ simulates a task of dailyliving comprising a scenario wherein the avatar 270′, which iscontrolled by the subject 108, is removing an object 248 (e.g., a cerealbox) from a kitchen cabinet 250. Similar to that described above inconjunction with FIG. 40, the avatar image 270′ on the screen 168represents and is manipulated by the subject 108 disposed on the forcemeasurement assembly 102 or the instrumented treadmill 600. The animatedmovement of the avatar image 270′ on the screen 168 is controlled basedupon the positional information acquired by the motionacquisition/capture system 300 described above, as well as the forceand/or moment data acquired from the force measurement assembly 102 orthe instrumented treadmill 600. In other words, the manner in which theavatar 270′ removes cereal box 248 from the kitchen cabinet 250 iscontrolled based upon the subject's detected motion. Similar to thatexplained above for FIG. 40, a disorder in a particular subject'smovement may be animated in the virtual reality environment 246′ bymaking the avatar's left arm 274 turn a different color (e.g., red). Assuch, any detected movement disorder is brought to the attention of thesubject 108 and the clinician conducting the evaluation and/or trainingof the subject. In this virtual reality scenario 246′, the cameras 302of the motion acquisition/capture system 300 may also be used to detectthe head movement of the subject 108 in order to determine whether ornot the subject is looking in the right direction when he or she isremoving the cereal box 248 from the kitchen cabinet 250. That is, thecameras 302 may be used to track the direction of the subject's gaze. Itis also to be understood that, in addition to the cameras 302 of FIGS.32 and 33, a head-mounted camera on the subject 108 may be used to trackthe subject's gaze direction. The head-mounted camera could also besubstituted for one or more of the cameras in FIGS. 32 and 33.

In yet further embodiments of the invention incorporating the avatar270, 270′ on the screen 168, the data acquisition/data processing device104 is specially programmed so as to enable a system user (e.g., aclinician) to selectively choose customizable biofeedback options in thevirtual reality scenarios 246′ and 268. For example, the clinician mayselectively choose whether or not the color of the avatar's foot or armwould be changed in the virtual reality scenarios 246′, 268 so as toindicate a disorder in the subject's movement. As another example, theclinician may selectively choose whether or not the dashed image of anavatar having normal gait could be displayed on the screen 168 togetherwith the avatar 270, 270′ so as to provide a means of comparison betweena particular subject's gait and that of a “normal” subject.Advantageously, these customizable biofeedback options may be used bythe clinician to readily ascertain the manner in which a particularsubject deviates from normal movement(s), thereby permitting theclinician to focus the subject's training on the aspects of thesubject's movement requiring the most correction.

In other further embodiments of the invention, the force measurementsystem 100 described herein is used for assessing the visual flow of aparticular subject, and at least in cases, the impact of a subject'svisual flow on the vestibular systems. In one or more exemplaryembodiments, the assessment of visual flow is concerned with determininghow well a subject's eyes are capable of tracking a moving object.

In still further embodiments, the force measurement system 100 describedherein is used for balance sensory isolation, namely selectivelyisolating or eliminating one or more pathways of reference (i.e.,proprioceptive, visual, and vestibular). As such, it is possible toisolate the particular deficiencies of a subject. For example, theelderly tend to rely too heavily upon visual feedback in maintainingtheir balance. Advantageously, tests performed using the forcemeasurement system 100 described herein could reveal an elderly person'sheavy reliance upon his or her visual inputs. In yet furtherembodiments, the virtual reality scenarios described above may includereaction time training and hand/eye coordination training (e.g.,catching a thrown ball, looking and reaching for an object, etc.). Inorder to effectively carry out the reaction time training routines andthe hand/eye coordination training routines, the system 100 could beprovided with the motion capture system 300 described above, as well aseye movement tracking system for tracking the eye movement (gaze) of thesubject or patient.

In yet further embodiments, the data acquisition/data processing device104 of the force measurement system 100 is programmed to determine apresence of a measurement error resulting from a portion of the loadfrom the at least one portion of the body of the subject 108 beingapplied to an external object rather than the intended top surfaces 114,116 of the force measurement assembly 102. As illustrated in the graphsof FIGS. 56-58, the data acquisition/data processing device 104 may beconfigured to determine the presence of the measurement error bycomputing a maximum drop in the vertical component (F_(Z)) of the outputforce for a predetermined duration of time. Also, as illustrated in thegraphs of FIGS. 56-58, the data acquisition/data processing device 104may be configured to determine the presence of the measurement error bycomputing an average drop in the vertical component (F_(Z)) of theoutput force for a predetermined duration of time. For example, avertical force curve (i.e., an F_(Z) curve) generated for a test trialwhere the subject 108 is pulling on the harness 352 while standing stillis illustrated in FIG. 56. As shown in this figure, the y-axis 362 ofthe graph 360 is the vertical component (F_(Z)) of the output force inNewtons (N), while the x-axis 364 of the graph 360 is the time inseconds (sec). In the graph 360 of FIG. 56, it can be seen that thevertical force curve 366 has a minimum point at 368. As another example,a vertical force curve (i.e., an F_(Z) curve) generated for a test trialwhere the subject 108 steps off the force measurement assembly 102 withone foot, and places his or her foot back onto the force measurementassembly 102, is illustrated in FIG. 57. As shown in this figure, they-axis 372 of the graph 370 is the vertical component (F_(Z)) of theoutput force in Newtons (N), while the x-axis 374 of the graph 370 isthe time in seconds (sec). In the graph 370 of FIG. 57, it can be seenthat the vertical force curve 376 has a minimum point at 378. As yetanother example, a vertical force curve (i.e., an F_(Z) curve) generatedfor a test trial where the subject 108 steps off the force measurementassembly 102 with both feet, but does not return to the forcemeasurement assembly 102, is illustrated in FIG. 58. As shown in thisfigure, the y-axis 382 of the graph 380 is the vertical component(F_(Z)) of the output force in Newtons (N), while the x-axis 384 of thegraph 380 is the time in seconds (sec). In the graph 380 of FIG. 58, itcan be seen that the vertical force curve 386 has a minimum point andendpoint at 388 where the subject 108 steps off the force measurementassembly 102 with both feet.

In these further embodiments, the force measurement system 100 mayfurther comprise an external force sensor (i.e., a load transducer)configured to measure a force exerted on an external object by thesubject. The external force sensor (i.e., a load transducer) isoperatively coupled to the data acquisition/data processing device 104of the force measurement system 100 so that the load data acquired bythe external force sensor (i.e., a load transducer) may be transmittedto the data acquisition/data processing device 104. When the externalforce sensor is used to measure the force exerted on the external objectby the subject, the data acquisition/data processing device 104 may beconfigured to determine the presence of the measurement error bydetermining whether the force measured by the external force sensor isgreater than a predetermined threshold value (e.g., greater than 10Newtons). In the illustrative embodiment, with reference to FIG. 54, theexternal object on which the subject 108 is exerting the force maycomprise a safety harness 352 worn by the subject 108 to prevent thesubject from falling, and the safety harness 352 may be provided withthe external force sensor 350 (see FIGS. 54 and 55). As shown in FIGS.54 and 55, the external force sensor 350 may be connected between theharness support structure 128′ and the safety harness 352. Moreparticularly, in the illustrative embodiment, the top of the externalforce sensor 350 is connected to the harness support structure 128′ bythe upper harness connectors 354, and the bottom of the external forcesensor 350 is connected to the harness ropes 358 by the lower harnessconnectors 356. The safety harness 352 is suspended from the lowerharness connectors 356 by the harness ropes 358. Also, in theillustrative embodiment, with reference now to FIG. 42, another externalobject on which the subject 108 is exerting the force may comprisestationary portions 122 a, 122 b of the base assembly 106 of the forcemeasurement system 100, and the stationary portions 122 a, 122 b of thebase assembly 106 may be provided with respective external force sensors390, 392 for measuring the forces exerted thereon by the subject 108. Inthe illustrative embodiment, the data acquisition/data processing device104 is further configured to classify the type of action by the subject108 that results in the subject 108 exerting the force on the externalobject (e.g., on the harness 352 or the stationary portions 122 a, 122 bof the base assembly 106). For example, in the illustrative embodiment,the type of action by the subject 108 that results in the subject 108exerting the force on the external object is selected from the groupconsisting of: (i) pulling on a safety harness 352, (ii) stepping atleast partially off the top surfaces 114, 116 of the force measurementassembly 102, and (iii) combinations thereof.

In these further embodiments, the data acquisition/data processingdevice 104 is further configured to generate an error notification onthe output screen of the operator visual display device 130 when thedata acquisition/data processing device 104 determines the presence ofthe measurement error. In addition, the data acquisition/data processingdevice 104 may be further configured to classify the type of action bythe subject 108 that results in the portion of the load being applied tothe external object (e.g., the harness 352 or the stationary portion 122a, 122 b of the base assembly 106). The error notification generated onthe output screen of the operator visual display device 130 by the dataacquisition/data processing device 104 may include the classification ofthe type of action by the subject 108 that results in the portion of theload being applied to the external object.

In these further embodiments, the data acquisition/data processingdevice 104 may compute the normalized maximum drop in the verticalcomponent (F_(Z)dropMAX) of the output force during a test trial byusing the following equation:

$\begin{matrix}{F_{Z}{{drop}{MAX}}{= \frac{\left( {{{Start}\;{{Mean}F}_{Z}} - {{Min}F_{Z}}} \right)}{{Start}\;{{Mean}F}_{Z}}}} & (14)\end{matrix}$where:StartMean F_(Z): mean value of the vertical force (F_(Z)) for the first500 milliseconds of the trial; andMin F_(Z): minimum value of the vertical force (F_(Z)) for the trial.For example, for the vertical force curve 366 depicted in FIG. 56, theF_(Z)dropMAX value is approximately 27.8% for the trial in which thesubject 108 is pulling on the harness 352 while standing still. Asanother example, for the vertical force curve 376 depicted in FIG. 57,the F_(Z)dropMAX value is approximately 78.3% for the trial in which thesubject 108 steps off the force measurement assembly 102 with one foot,and then places his or her foot back onto the force measurement assembly102. As yet another example, for the vertical force curve 386 depictedin FIG. 58, the F_(Z)dropMAX value is approximately 95.0% for the trialin which the subject 108 steps off the force measurement assembly 102with both feet, and does not return to the force measurement assembly102.

In these further embodiments, the data acquisition/data processingdevice 104 may compute the normalized average drop in the verticalcomponent (F_(Z)dropAVG) of the output force during a test trial byusing the following equation:

$\begin{matrix}{{F_{Z}{{drop}{AVG}}} = \frac{\left( {{{Start}\;{{Mean}F}_{Z}} - {{Mean}F}_{Z}} \right)}{{Start}\;{{Mean}F}_{Z}}} & (15)\end{matrix}$where:StartMean F_(Z): mean value of the vertical force (F_(Z)) for the first500 milliseconds of the trial; andMean F_(Z): mean value of the vertical force (F_(Z)) from 501milliseconds to the end of the trial.For example, for the vertical force curve 366 depicted in FIG. 56, theF_(Z)dropAVG value is approximately 2.7% for the trial in which thesubject 108 is pulling on the harness 352 while standing still. Asanother example, for the vertical force curve 376 depicted in FIG. 57,the F_(Z)dropAVG value is approximately 3.8% for the trial in which thesubject 108 steps off the force measurement assembly 102 with one foot,and then places his or her foot back onto the force measurement assembly102. As yet another example, for the vertical force curve 386 depictedin FIG. 58, the F_(Z)dropAVG value is approximately 4.7% for the trialin which the subject 108 steps off the force measurement assembly 102with both feet, and does not return to the force measurement assembly102.

In these further embodiments, the data acquisition/data processingdevice 104 may be configured to generate an error notification on theoutput screen of the operator visual display device 130 based uponcomparing the F_(Z)dropMAX and F_(Z)dropAVG values computed for aparticular trial to predetermined threshold values. For example, thedata acquisition/data processing device 104 may be configured todetermine if the F_(Z)dropMAX value computed for a particular trial isgreater than 0.50 and if the F_(Z)dropAVG value computed for aparticular trial is greater than 0.02. When the data acquisition/dataprocessing device 104 determines that the F_(Z)dropMAX value is greaterthan 0.50 and the F_(Z)dropAVG value is greater than 0.02 (i.e., both ofthese two conditions are true), the error notification outputted by thedata acquisition/data processing device 104 on the operator visualdisplay device 130 may indicate that the subject has likely fallenduring the trial (e.g., by outputting a message on the screen, such as“Subject has most likely fallen during trial, it is suggested that trialbe repeated.”). However, if the data acquisition/data processing device104 determines that the F_(Z)dropAVG value computed for a particulartrial is greater than 0.01, but at least one of the preceding twoconditions is not true (i.e., the F_(Z)dropMAX value is not greater than0.50 and/or the F_(Z)dropAVG value is not greater than 0.02), then theerror notification outputted by the data acquisition/data processingdevice 104 on the operator visual display device 130 may indicate thatthe subject has likely pulled on the harness 352 (e.g., by outputting amessage on the screen, such as “Subject has most likely pulled onharness, it is suggested that trial be repeated.”). Otherwise, if thedata acquisition/data processing device 104 determines that the firstset criteria are not satisfied (i.e., F_(Z)dropMAX value is less than0.50 and/or F_(Z)dropAVG value is less than 0.02) and the secondcriteria are not satisfied (i.e., F_(Z)dropAVG value is less than 0.01),then no error notification will be outputted by the dataacquisition/data processing device 104 on the operator visual displaydevice 130 because, based on the computed F_(Z)dropMAX and F_(Z)dropAVGvalues, it appears to have been a good trial.

In still further embodiments, the data acquisition/data processingdevice 104 of the force measurement system is programmed to determine atype of balance strategy that the subject is using to maintain his orher balance on the force measurement assembly. In these furtherembodiments, the type of balance strategy determined by the dataacquisition/data processing device 104 is selected from the groupconsisting of: (i) an ankle strategy, (ii) a hip strategy, (iii) a stepstrategy, and (iv) combinations thereof. As will be describedhereinafter, the data acquisition/data processing device 104 maydetermine the type of balance strategy that the subject is using tomaintain his or her balance on the force measurement assembly by usingoutput data from a variety of different devices. In one or more of thesefurther embodiments, the force measurement assembly may be in the formof a force plate or a balance plate (e.g., the displaceable force plate102 depicted in FIG. 44 or the static force plate 102′ depicted in FIG.52). When the force measurement assembly is in the form of thedisplaceable force plate 102 depicted in FIG. 44, the force measurementsystem further includes the base assembly 106 described above, which hasa stationary portion and a displaceable portion. In this arrangement, asdescribed above, the force measurement assembly 102 forms a part of thedisplaceable portion of the base assembly 106, and the force measurementsystem additionally comprises a plurality of actuators 158, 160 coupledto the data acquisition/data processing device 104. As explained above,the first actuator 158 is configured to translate the displaceableportion of the base assembly 106, which includes the force measurementassembly 102, relative to the stationary portion of the base assembly106, while the second actuator 160 is configured to rotate the forcemeasurement assembly 102 about a transverse rotational axis TA relativeto the stationary portion of the base assembly 106.

In these further embodiments, the best type of balance strategy that canbe employed by the subject depends on the particular task that thesubject is being asked to perform. That is, for one particular task, anankle balance strategy may be the best strategy for the subject to use,while for another particular task, a hip balance strategy may be thebest strategy for the subject to use. For other tasks, a step balancestrategy may be the best option for the subject. For example, becausethe ankle balance strategy does not offer as much opportunity to changethe subject's center of gravity, it is not the best balance option forall situations. Also, a particular subject may have physical limitationsthat affect his or her balance strategy (e.g., an older person withstiff joints may have a significantly harder time using an ankle balancestrategy as compared to a younger person with more flexible joints).

In one or more other further embodiments, the force measurement assemblymay be in the form of an instrumented treadmill 600 (see FIG. 38),rather than a force measurement assembly 102, 102′.

In one or more of these further embodiments, the data acquisition/dataprocessing device 104 is programmed to determine the type of balancestrategy that the subject is using to maintain his or her balance on theforce measurement assembly based upon one or more of the output forcesand/or moments determined from the one or more signals of the forcemeasurement assembly (i.e., the one or more signals of the forcemeasurement assembly 102, 102′ or instrumented treadmill 600). In thesefurther embodiments, the one or more output forces and/or moments usedby the data acquisition/data processing device 104 to determine the typeof balance strategy comprise one or more shear forces, one or morevertical forces, or one or more moments used to compute the center ofpressure of the subject. For example, when the data acquisition/dataprocessing device 104 utilizes the shear force or a parameter based onthe shear force to determine the type of balance strategy, a shear forceapproximately equal to zero is representative of an all ankle strategyby the subject, whereas a shear force that is equal to a substantialnon-zero value is indicative of a hip strategy by the subject. In such acase, if the shear force measured by the force measurement assembly isgreater than a predetermined magnitude, then the subject is using his orher hips, rather than his or her ankles, to maintain balance. The dataacquisition/data processing device 104 may determine if the subject 108uses a step balance strategy by evaluating the center of pressure of thesubject 108 determined from the force measurement assembly (i.e., a stepby the subject 108 will be evident by a characteristic change in thecenter of pressure of the subject).

In another one or more of these further embodiments, the forcemeasurement system may further comprise a motion capture system with oneor more motion capture devices configured to detect the motion of thesubject 108 (e.g., the marker-based motion capture system 300 withcameras 302 depicted in FIGS. 32 and 33). In these further embodiments,the motion capture system 300 is operatively coupled to the dataacquisition/data processing device 104, and the data acquisition/dataprocessing device 104 is programmed to determine the type of balancestrategy that the subject 108 is using to maintain his or her balance onthe force measurement assembly based upon the output data from the oneor more motion capture devices of the motion capture system (i.e., thelimb movements of the subject determined from the motion capture data).For example, when the data acquisition/data processing device 104utilizes the motion capture system to determine the type of balancestrategy, the images captured by the motion capture system areindicative of whether the subject 108 is using a hip strategy or anankle strategy to maintain his or her balance.

In yet another one or more of these further embodiments, the forcemeasurement system may further comprise at least one camera (e.g., atleast one web camera) configured to capture the motion of the subject108. In these further embodiments, the camera is operatively coupled tothe data acquisition/data processing device 104, and the dataacquisition/data processing device 104 is programmed to determine thetype of balance strategy that the subject 108 is using to maintain hisor her balance on the force measurement assembly based upon the outputdata from the at least one camera. For example, when the dataacquisition/data processing device 104 utilizes the at least one camera(e.g., at least one web camera) to determine the type of balancestrategy, a vision model (e.g., PoseNet) that employs a convolutionalneural network (CNN) may be used to estimate the balance strategy of thesubject by estimating the locations of the key body joints of thesubject 108. In one or more of these further embodiments, a markerlessmotion capture system comprising a plurality of cameras (e.g., aplurality of web cameras) may be mounted on elements of the forcemeasurement system in order to capture the motion of the subject in avariety of different planes. For example, with reference to FIG. 44, afirst camera may be mounted on the screen 168 facing the subject inorder to capture the coronal plane of the subject. A second camera maybe mounted on the first side bar of the harness support structure 128′(see FIG. 54), and angled in a direction facing the subject so as tocapture the sagittal plane of the subject from a first side. A thirdcamera may be mounted on the second side bar of the harness supportstructure 128′ (see FIG. 54), and angled in a direction facing thesubject so as to capture the sagittal plane of the subject from a secondside.

In still another one or more of these further embodiments, the forcemeasurement system may further comprise one or more inertial measurementunits (e.g., one or more inertial measurement units 306 as depicted inFIG. 49) configured to detect the motion of the subject 108. In thesefurther embodiments, the one or more inertial measurement units 306 areoperatively coupled to the data acquisition/data processing device 104,and the data acquisition/data processing device 104 is programmed todetermine the type of balance strategy that the subject 108 is using tomaintain his or her balance on the force measurement assembly based uponthe output data from the one or more inertial measurement units 306. Forexample, when the data acquisition/data processing device 104 utilizesone or more inertial measurement units 306 to determine the type ofbalance strategy, a first one of the inertial measurement units 306 maybe mounted on the torso of the subject 108, a second one of the inertialmeasurement units 306 may be mounted near a hip of the subject 108, anda third one of the inertial measurement units 306 may be mounted near anankle of the subject 108 (e.g., refer to FIG. 49).

In yet another one or more of these further embodiments, the forcemeasurement system may further comprise a radar-based sensor configuredto detect the posture of the subject 108. In these further embodiments,the radar-based sensor is operatively coupled to the dataacquisition/data processing device 104, and the data acquisition/dataprocessing device 104 is programmed to determine the type of balancestrategy that the subject 108 is using to maintain his or her balance onthe force measurement assembly based upon the output data from theradar-based sensor. For example, when the data acquisition/dataprocessing device 104 utilizes the radar-based sensor to determine thetype of balance strategy, the radar-based sensor may be mounted on oneof the side bars of the harness support structure 128′ (see FIG. 54),and angled in a direction facing the subject so as to capture thesagittal plane of the subject from a side. As one example, theradar-based sensor may utilize a miniature radar chip to detecttouchless gesture or pose interactions, such as in the Google® Solidevice.

In still another one or more of these further embodiments, the forcemeasurement system may further comprise an infrared sensor configured todetect the posture of the subject 108. In these further embodiments, theinfrared sensor is operatively coupled to the data acquisition/dataprocessing device 104, and the data acquisition/data processing device104 is programmed to determine the type of balance strategy that thesubject 108 is using to maintain his or her balance on the forcemeasurement assembly based upon the output data from the infraredsensor. For example, as described above, the infrared sensor may be partof a motion detection/motion capture system that employs infrared light(e.g., the system could utilize an infrared (IR) emitter to project aplurality of dots onto objects in a particular space as part of amarkless motion capture system). As shown in the exemplary system ofFIG. 50, the motion detection/motion capture system employing infraredlight may comprise one or more cameras 320, one or more infrared (IR)depth sensors 322, and one or more microphones 324 to provide full-bodythree-dimensional (3D) motion capture, facial recognition, and voicerecognition capabilities.

In these further embodiments where the balance strategy of the subject108 is determined, the force measurement system further comprises atleast one visual display device having an output screen (e.g., thesubject visual display device 107 and/or operator visual display device130 described above and depicted in FIG. 1). In these furtherembodiments, the data acquisition/data processing device 104 isconfigured to generate a visual indicator (e.g., see the virtualrepresentation 394 in FIGS. 59 and 60) indicative of the type of balancestrategy that the subject is using to maintain his or her balance, andto display the visual indicator 394 in the one or more images 396, 397on the output screen of the at least one visual display device.

In these further embodiments where the balance strategy of the subject108 is determined, the force measurement system further comprises one ormore user input devices, such as the keyboard 132 and/or mouse 134depicted in FIG. 1 and described above. In these further embodiments,the user input device 132, 134 is configured to output an input devicesignal based upon an input by a user, and the data acquisition/dataprocessing device 104 is configured to set a parameter related to thebalance strategy of the subject 108 based upon the input by the userentered using the user input device 132, 134. Also, in these furtherembodiments, the data acquisition/data processing device 104 is furtherprogrammed to generate and display visual feedback to the subject 108 onthe output screen of the at least one visual display device based uponthe parameter entered by the user. For example, the clinician may set agoal for a particular angle of displacement of the subject's hip angleθ_(H) or the subject's ankle angle θ_(A), and then a line may bedisplayed on the subject visual display device that denotes thatparticular angle. As the subject displaces his or her body on the forcemeasurement assembly, the virtual representation 394 of the subject onthe force plate surface 398 disposed in the screen image 396, 397 may bedisplaced in accordance with the subject's movement so that the subject108 is able to visualize the virtual representation 394 of him or herapproach the line marking his or her joint angle displacement goal.

In these further embodiments, the visual feedback provided to thesubject 108 regarding his or her balance strategy may be provided inconjunction with a balance assessment and training regime. First of all,an assessment may be performed on the subject to determine if there areparticular weaknesses in the balance strategy of the subject. Forexample, as described above, a motion capture system may be used todetermine the hip and ankle joint angles θ_(H), θ_(A) of the subject inthe sagittal plane. Secondly, based on the results of the balanceassessment, a balance training program for the subject may be developed.For example, the balance training program may involve scenarios thatwould require the subject to use each one of the three balancestrategies (i.e., the ankle strategy, the hip strategy, and the stepstrategy) depending on the scenario. During the training, the clinicianmay use the visual feedback functionality of the force measurementsystem in order to set the required range of motion for the subject(e.g., the angular range of displacement for the hip joint angle and/orthe ankle joint angle of the subject). Then, during the training, thevisual feedback may be modified when the subject reaches a certaintarget angular displacement (e.g., the line displayed on the subjectvisual display device that denotes a particular goal angle may beshifted to another rotational position once the goal is achieved). Thedata acquisition/data processing device 104 of the force measurementsystem may be programmed to perform all of the above-describedassessment and training functionality.

In FIG. 59, a first exemplary screen image 396 on the subject visualdisplay device 107 is illustrated. In the screen image 396 of FIG. 59,the virtual representation 394 of the subject is depicted using an anklebalance strategy where the hip joint angle θ_(H) is approximately equalto the ankle joint angle θ_(A). In FIG. 60, a second exemplary screenimage 397 on the subject visual display device 107 is illustrated. Inthe screen image 397 of FIG. 60, the virtual representation 394 of thesubject is depicted using a combination hip and ankle balance strategywhere the hip joint angle θ_(H) is not equal to the ankle joint angleθ_(A). In general, when the hip joint angle θ_(H) is equal orapproximately equal to the ankle joint angle θ_(A), then an anklebalance strategy is being used by the subject. Conversely, when the hipjoint angle θ_(H) and the ankle joint angle θ_(A) are different, then ahip balance strategy is being used by the subject.

In yet further embodiments, referring to FIGS. 61 and 62, the forcemeasurement system generally comprises a force measurement assembly 102configured to receive a subject 108, at least one visual display device344, 348, the at least one visual display device 344, 348 configured todisplay one or more images; and one or more data processing devices 104operatively coupled to the force measurement assembly 102 and the atleast one visual display device 344, 348. In these further embodiments,as shown in FIGS. 61 and 62, the one or more data processing devices 104are further configured to generate a first image portion 349, 355 anddisplay the first image portion 349, 355 using the at least one visualdisplay device 344, 348, and to generate a second image portion 351, 357and display the second image portion 351, 357 using the at least onevisual display device 344. The first image portion 349, 355 displayedusing the at least one visual display device 344, 348 comprises aprimary screen image for viewing by the subject 108, and the secondimage portion 351, 357 displayed using the at least one visual displaydevice 344 comprises a virtual screen surround configured to at leastpartially circumscribe three sides of a torso of the subject 108 and tosubstantially encompass a peripheral vision of the subject 108.

As shown in FIGS. 61 and 62, in the illustrative embodiments, the forcemeasurement assembly 102 is in the form of a force plate or a balanceplate. Although, in other embodiments, the force measurement assemblymay be in the form of an instrumented treadmill (e.g., the instrumentedtreadmill 600, 600′ shown in FIGS. 38 and 45). Also, in the embodimentsof FIGS. 61 and 62, the force measurement system further includes thebase assembly 106 described above, which has a stationary portion and adisplaceable portion. In this arrangement, as described above, the forcemeasurement assembly 102 forms a part of the displaceable portion of thebase assembly 106, and the force measurement system additionallycomprises a plurality of actuators 158, 160 coupled to the one or moredata processing devices 104. As explained above, the first actuator 158is configured to translate the displaceable portion of the base assembly106, which includes the force measurement assembly 102, relative to thestationary portion of the base assembly 106, while the second actuator160 is configured to rotate the force measurement assembly 102 on therotatable carriage assembly 157 about a transverse rotational axis TArelative to the stationary portion of the base assembly 106 (see e.g.,FIGS. 3, 42, and 43).

Now, with reference to FIG. 61, in one further embodiment, the at leastone visual display device 344, 348 comprises a first visual displaydevice 348 and a second visual display device 344. In the embodiment ofFIG. 61, it can be seen that the first visual display device comprises aflat display screen 348. In other embodiments, the first visual displaydevice may alternatively comprise a curved display screen. As shown inFIG. 61, the first image portion 349 with the primary screen image isdisplayed on the flat display screen 348 of the first visual displaydevice. In the embodiment of FIG. 61, it can be seen that the secondvisual display device is in the form of a head-mounted visual displaydevice 344. For example, in the embodiment of FIG. 61, the head-mountedvisual display device 344 may comprise an augmented reality headset thatis capable of supplementing real-world objects, such as the flat displayscreen 348, with computer-generated virtual objects. The head-mountedvisual display device 344 may have the headset performance parametersdescribed above (e.g., the aforedescribed field of view range, refreshrate range, and display latency range). As shown in FIG. 61, the secondimage portion 351 with the virtual screen surround is displayed usingthe head-mounted visual display device 344. Advantageously, similar tothe physical dome-shaped projection screen 168 described above, thevirtual screen surround 351 is capable of creating an immersiveenvironment for the subject 108 disposed on the force measurementassembly 102 (i.e., the virtual screen surround 351 engages enough ofthe subject's peripheral vision such that the subject becomes, andremains immersed in the primary screen image that is being displayed onthe flat display screen 348).

Next, with reference to FIG. 62, in another further embodiment, the atleast one visual display device comprises the head-mounted visualdisplay device 344 without a physical display device. As shown in FIG.62, the first image portion 355 with the primary screen image isdisplayed using the head-mounted visual display device 344. In FIG. 62,the second image portion with the virtual screen surround 357 isadditionally displayed using the head-mounted visual display device 344.In the embodiment of FIG. 62, the head-mounted visual display device 344may comprise a virtual reality headset that generates entirely virtualobjects or an augmented reality headset that is capable of supplementingreal-world objects with computer-generated virtual objects.

In the embodiments of FIGS. 61 and 62, it can be seen that the virtualscreen surround 351, 357 generated by the one or more data processingdevices 104 and displayed by the at least one visual display device 344comprises a virtual cutout 353, 359 configured to receive a portion ofthe body of the subject 108 therein. Similar to that described above forthe cutout 178 in the physical dome-shaped projection screen 168, thesemi-circular virtual cutout 353, 359 permits the subject 108 to besubstantially circumscribed by the generally hemispherical virtualscreen surround 351, 357 on three sides. Also, in the embodiments ofFIGS. 61 and 62, the virtual screen surround 351, 357 generated by theone or more data processing devices 104 and displayed by the at leastone visual display device 344 has a concave shape. More specifically, inthe illustrative embodiments of FIGS. 61 and 62, the virtual screensurround 351, 357 generated by the one or more data processing devices104 and displayed by the at least one visual display device 344, 348 hasa hemispherical shape.

In addition, as shown in the embodiments of FIGS. 61 and 62, the primaryscreen image 349, 355 in the first image portion may comprise a subjecttest screen or subject training screen with a plurality of targets ormarkers 238 (e.g., in the form of circles) and a displaceable visualindicator or cursor 240. As described above, the one or more dataprocessing devices 104 control the movement of the visual indicator 240towards the plurality of stationary targets or markers 238 based uponoutput data determined from the output signals of the force transducersassociated with the force measurement assembly 102. For example, in onetesting or training scenario, the subject 108 may be instructed to movethe cursor 240 towards each of the plurality of targets or markers 238in succession. For example, the subject 108 may be instructed to movethe cursor 240 towards successive targets 238 in a clockwise fashion(e.g., beginning with the topmost target 238 in the primary screen image349, 355).

In one or more other embodiments, rather than comprising a subject testscreen or subject training screen, the primary screen image 349, 355 inthe first image portion displayed by the at least one visual displaydevice 344, 348 may alternatively comprise one of: (i) an instructionalscreen for the subject, (ii) a game screen, and (iii) an immersiveenvironment or virtual reality environment.

In these further embodiments, the virtual screen surround 351, 357depicted in FIGS. 61 and 62 may be displaced by the one or more dataprocessing devices 104 in order to compensate for the movement of thehead of the subject 108. For example, a head position detection device(e.g., an inertial measurement unit 306 as depicted in FIG. 50) may beprovided on the head of the subject 108 in order to measure the positionof the head of the subject 108, and then the one or more data processingdevices 104 may adjust the position of the virtual screen surround 351,357 in accordance with the subject's head position so that the virtualscreen surround 351, 357 always substantially encompasses a peripheralvision of the subject regardless of the gazing direction of the subject108. In other words, the virtual screen surround 351, 357 rotates withthe head of the subject 108 so that the subject 108 is always generallygazing at the center portion of the virtual screen surround 351, 357(i.e., the one or more data processing devices 104 displace the virtualscreen surround 351, 357 to track the position of the subject's head).

In other embodiments, rather than an inertial measurement unit, the headposition measurement device for measuring the head position of thesubject 108 may comprise one or more of the following: (i) a videocamera, (ii) an infrared sensor, (iii) an ultrasonic sensor, and (iv) amarkerless motion capture device.

Also, in these further embodiments, the one or more data processingdevices 104 may be programmed to activate or turn “on” the virtualscreen surround 351, 357 in FIGS. 61 and 62 when the weight of thesubject 108 is detected on the force measurement assembly 102 (e.g.,when the force measurement assembly 102 detects a vertical force F_(Z)that meets or exceeds a predetermined threshold value, for example,F_(Z)>200 Newtons). Conversely, the one or more data processing devices104 may be programmed to deactivate or turn “off” the virtual screensurround 351, 357 in FIGS. 61 and 62 when the weight of the subject 108is not detected on the force measurement assembly 102 (e.g., when theforce measurement assembly 102 detects a vertical force F_(Z) that isless than a predetermined threshold value, for example, F_(Z)<200Newtons). Also, the one or more data processing devices 104 may beprogrammed to deactivate or turn “off” the virtual screen surround 351,357 in FIGS. 61 and 62 if it is determined that the subject 108 haslikely fallen during testing or training (e.g., when the one or moreprocessing devices 104 determine that the F_(Z)dropMAX value is greaterthan 0.50 and the F_(Z)dropAVG value is greater than 0.02 as explainedabove).

In addition, in these further embodiments, the one or more dataprocessing devices 104 may be programmed to visually indicate when thesubject 108 is placing an excessive amount of weight (e.g., greater than60% of his or her body weight) on one of his or her feet compared to theother of his or her feet. For example, when the subject 108 in FIGS. 61and 62 is placing an excessive amount of the weight (e.g., greater than60% of his or her body weight) on his left foot as detected by the firstplate component 110 (i.e., the left plate component 110) of the dualforce plate 102, the one or more data processing devices 104 may beprogrammed to make the left half of the virtual screen surround 351, 357brighter and/or change the color of the left half of the virtual screensurround 351, 357 (e.g., change the color to “red”). Similarly, in thisexample, when the subject 108 in FIGS. 61 and 62 is placing an excessiveamount of the weight (e.g., greater than 60% of his or her body weight)on his right foot as detected by the second plate component 112 (i.e.,the right plate component 112) of the dual force plate 102, the one ormore data processing devices 104 may be programmed to make the righthalf of the virtual screen surround 351, 357 brighter and/or change thecolor of the right half of the virtual screen surround 351, 357 (e.g.,change the color to “red”).

In these further embodiments, the data acquisition/data processingdevice 104 may be further programmed to generate a virtualrepresentation of the subject and a visual element with which thevirtual representation of the subject is able to interact, and todisplay the virtual representation of the subject and the visual elementin the one or more images on the output screen of the at least onevisual display device (e.g., the subject visual display device 107). Forexample, as described above with regard to FIG. 41, a virtualrepresentation of the subject (e.g., an avatar 270′) may interact with avisual element (e.g., a cereal box 248 in a kitchen cabinet 250) in avirtual reality scene. As another example, as illustrated in FIG. 15, avirtual representation of the subject 204 may interact with another typea visual element (e.g., a bridge 207) in a virtual reality scene. Inthese embodiments, the data acquisition/data processing device 104 maybe further programmed to generate tactile feedback for the subject 108using at least one of the first and second actuators 158, 160 on thebase assembly 106 based upon the virtual representation of the subjectinteracting with the visual element in the one or more images on theoutput screen of the at least one visual display device (e.g., in thebridge scene 206, if the virtual representation of the subject 204 iswalking up an incline on the bridge 207, the second actuator 160 mayrotate the force measurement assembly 102 relative to the base assembly106 so as to simulate the incline of the bridge 207 in the scene 206).In some of these embodiments, the visual element in the one or moreimages on the output screen of the at least one visual display devicemay comprise an obstacle disposed in a virtual walking path of thevirtual representation of the subject, and the data acquisition/dataprocessing device 104 may be programmed to generate the tactile feedbackfor the subject 108 using the at least one of the first and secondactuators 158, 160 on the base assembly 106 when the virtualrepresentation of the subject on the output screen collides with theobstacle disposed in the virtual walking path in the one or more imagesdisplayed on the at least one visual display device (e.g., in the bridgescene 206, if the virtual representation of the subject 204 collideswith one of the sides of the bridge 207, the subject 108 will receive aslight jolt from one of the actuators 158, 160). As another example, ifthe virtual representation of the subject is walking down an endlessgrocery aisle and collides with a box in the grocery aisle, the firstactuator 158 of the base assembly 106 may be used to provide a slightjolt to the subject 108 to indicate the collision.

Now, with reference to the block diagrams in FIGS. 63 and 64, severalillustrative biomechanical analysis systems in which the aforedescribedforce measurement assembly 102 or instrumented treadmill 600, 600′ areused with a three-dimensional (3D) pose estimation system will beexplained. In these one or more illustrative embodiments, the 3D poseestimation system may comprise the 3D pose estimation system describedin U.S. Pat. No. 10,853,970, the entire disclosure of which isincorporated herein by reference. Initially, in the block diagram 710 ofFIG. 63, it can be seen that the 3D pose estimation system 716 receivesimages of a scene from one or more RGB video cameras 714. The 3D poseestimation system 716 extracts the features from the images of the scenefor providing inputs to a convolutional neural network. Then, the 3Dpose estimation system 716 generates one or more volumetric heatmapsusing the convolutional neural network, and applies a maximizationfunction to the one or more volumetric heatmaps in order to obtain athree dimensional pose of one or more persons in the scene. As shown inFIG. 63, the 3D pose estimation system 716 determines one or more threedimensional coordinates of the one or more persons in the scene for eachimage frame, and outputs the three dimensional coordinates to a kineticcore software development kit (SDK). In addition, as shown in FIG. 63,user input and/or calibration parameters 712 may also be received asinputs to the 3D pose estimation system 716.

In the illustrative embodiment of FIG. 63, in addition to the threedimensional coordinates for each image frame from the 3D pose estimationsystem 716, the kinetic core SDK 718 may also receive one or more devicesignals 720 from one or more force plates and/or an instrumentedtreadmill and/or as inputs. For example, the instrumented treadmill andthe one or more force plates may comprise the force measurement assembly102 or the instrumented treadmill 600, 600′ described above. Inaddition, as shown in FIG. 63, the kinetic core SDK 718 may receive amonitor/display signal 722 as an input (e.g., an input signal from atouchscreen display). Further, as shown in FIG. 63, the kinetic core SDK718 may receive one or more motion base signals 724 (e.g., one or moresignals from the base assembly 106 described above). Then, the kineticcore SDK 718 determines and outputs one or more biomechanicalperformance parameters in an application desired output/report 726 usingthe three dimensional coordinates from the 3D pose estimation system 716and the one or more signals 720, 722, 724 from the connected devices.The illustrative biomechanical analysis system of FIG. 63 does notinclude trained CNN backpropagation, but another illustrativebiomechanical analysis system that will be described hereinafter doesinclude trained CNN backpropagation.

Next, referring to FIG. 64, a second illustrative biomechanical analysissystem in which the pose estimation system may be utilized will beexplained. With reference to the block diagram 730 of FIG. 64, it can beseen that the second illustrative biomechanical analysis system issimilar in many respects to the first illustrative biomechanicalanalysis system described above. As such, for the sake of brevity, thefeatures that the second illustrative biomechanical analysis system hasin common with the first illustrative biomechanical analysis system willnot be discussed because these features have already been explainedabove. Although, unlike the first illustrative biomechanical analysissystem, the second illustrative biomechanical analysis system of FIG. 64includes trained CNN backpropagation. More specifically, in theillustrative embodiment of FIG. 64, the kinetic core SDK 718 isoperatively coupled to one or more trained convolutional neural networks(CNNs) 717, which in turn, are operatively coupled to the 3D poseestimation system 716 so that better accuracy may be obtained from the3D pose estimation system 716. In the illustrative embodiment of FIG.64, in addition to the three dimensional coordinates for each imageframe from the 3D pose estimation system 64, the kinetic core SDK 718receives the device signals 720, 722, 724 from the connected externaldevices. Then, the kinetic core SDK 718 determines and outputs one ormore biomechanical performance parameters in a biomechanical outputreport 728 using the three dimensional coordinates from the 3D poseestimation system 716 and the signals 720, 722, 724 from the connectedexternal device. As shown in FIG. 64, the biomechanical output report728 may include annotated datasets and/or kinematic and kinetic profilesfor the one or more persons in the scene.

Now, the user input/calibration 712, the kinetic core SDK 718, and theapplication output 726 and 728 of the illustrative biomechanicalanalysis systems 710 and 730 will be described in further detail. In theillustrative embodiments described above, some user input 712 from thesystem may augment the automatic system calibration tasks performed. Onesource of input may involve the user selecting the XY pixel location ofthe four force plate corners from multiple RBG video images. Thelocations can be triangulated from this information. Additionalcalibration may require the user to hold an object, such as a checkboardor Aruco pattern. The person holding the calibration target will thenperform a sequence of tasks, moving the calibration target at theoptimal angle to the respective cameras and to the optimal positions forcalibration within the capture volume. Another form of calibration mayinvolve having the user standing on the force plate in the capturevolume. The system will capture the user rotating their body around thevertical axis with their arms at 45 degree and 90 degrees of shoulderabduction. The 3D pose estimation system 716 then calibrates based onthe plausible parameters (lengths) of the subject's body segment's andcombined shape.

In the illustrative embodiment of FIG. 64, there are one or more trainedCNN modules 717 which are used to obtain better accuracy of the 3D poseestimation system 716. One of these models may be a “plausible physics”model. This model determined the plausibility of the estimated pose inthe physical domain. In addition, this model may consider the temporalparameters of the physics, including: (i) body inertia, (ii)ground/floor contact in regards to foot position, (iii) body segmentlengths, (iv) body segment angular velocities, and (v) joint ranges ofmotion. In the illustrative embodiment, an additional CNN may be appliedfor allowable human poses. This is a general model which will preventunrealistic body representations and 3D reconstructions.

In the illustrative embodiments of FIGS. 63 and 64, the desiredapplication output 726, 728 is a biomechanical analysis of the action'sperformed in the capture volume. This includes output, such as anannotated dataset in which calculated values, such as the rate of forcedevelopment, maximum force, and other descriptors are displayed. Ageneral report of the movement performed may also be generated and thealgorithmically determined kinetic and kinematic insights from bothtraditional manually devised algorithms and insights derived frommachine learned algorithms obtained from analysis of large datasets ofsimilar movements.

The specific output is determined by the movement performed. As anexample, analyzing a baseball swing is quite different than analyzingthe balance of a subject after physical or visual perturbation. Each hasits own key performance indicators (KPIs).

Using the key point information from the 3D pose estimation system 716and the associated algorithms for movement specific analysis, the systembecomes an “expert system” which is capable of diagnosing and providingrehabilitation and training interventions to improve the subject'sperformance during the tasks performed in the capture volume. Thisrequires a large amount of training data, which is a recording of theactions performed in the capture space.

In the illustrative biomechanical analysis systems 710, 730 describedabove, the center of mass may be determined in order to guide the visualrepresentation of the person in the visual scene. Other desired outputsmay be trunk, knee, head position and hands position. With thesevariables' positions, angular and linear velocities can be calculatedand essential for balance estimations can be provided. Also, for afunctional force or balance plate where a subject can traverse theplate, the estimation of kinematic body segment position desiredvariables may be upper limb, trunk, hips, knees and ankle position.These variables would provide a gait analysis in combination with groundreaction force output provided by the force plate. The user can berequired to walk, walk over a step or variables of it, plus other rangeof motion activities. The segment positions will provide linear andangular velocities and general kinematic outputs.

The illustrative biomechanical analysis systems 710, 730 may furtherinclude training models provided as part of the systems that enable thebuilding of dynamic visual scenes. For example, when a participant usesthe system 710, 730 for the first time, he or she is asked to walk onthe treadmill or sway on the plate. Based on these movements the currentkinematics/kinetics, COM movements, ground reaction forces areestimated. This is used to build scenes, for example if while walkingthe subject does not lift his foot enough, the obstacle height in thevisual scene will be low at first. Different levels can then be builtinto the training protocol to progressively increase the obstacle heightand encourage the person to lift his leg at a required height. Inaddition, with upper limb position a system user can perform dual taskactivities similar to daily life activities, where he or she would bewalking or standing while pointing or grabbing objects. Such activitiescan be used as assessment and training as already proven by previousresearch.

In another illustrative biomechanical application, a therapist mayreview a captured video and force plate data, and write notes on theperformance of the subject and any thoughts regarding their condition.Additionally, the expert may provide a review kinematic analysis whileusing the force plate data as additional information for making thedecision. One key aspect of one biomechanical analysis system 710, 730is determining the sway strategy of the patient. The kinematicinformation, derived from the 3D pose estimation system 716 is used bythe therapist to determine a “sway strategy” or “balance strategy” ofthe patient. In the system, the subject is assumed to use an anklestrategy when regaining their balance in response to a knownperturbation of the floor. The therapist may use the kinematicinformation to rate the strategy and determine if the amount of ankleversus hip movement is acceptable for the test. If deemed acceptable,the strategy employed by the subject and the therapist annotation(acceptable sway strategy or not) will be saved and used to train thealgorithm. In time, the algorithm will provide instant feedback to thepatient on the acceptability of the trial's sway strategy and provide arecommendation on how to improve the strategy (i.e.; focus on bending atthe ankles and keep the torso upright, etc.). Also, the trunk and headposition of the patient can offer a differential analysis to balance andhow a patient performs a task. With the upper limb positions, a patientcan perform tasks related to hand-eye coordination, ranges of motion,and dual tasks. These tasks are known for assessment and training inseveral types of population from neurological to orthopedic.

In one or more illustrative embodiments, the performance of the usersuggestions on the sway strategy of the subsequent trial may be used toprovide more useful recommendations. By grading the performance on thesubsequent trial thousands of times, the machine learned algorithmlearns what to suggest to the patient to obtain the desired result.

For a functional force or balance plate where a subject can traverse theplate, the 3D pose estimation system 716 may be used to estimate gaitand upper body events during tasks, such as gait over obstacles, squatsand range of motion activities. Aligning with the ground reaction forcesprovided by the force plate, a clinician will be able to determine notonly body sway, but quantify errors in tasks, such as tandem gait.

In the illustrative biomechanical analysis systems 710, 730 describedabove, one or more data processing devices 104 may be configured topredict one or more balance parameters of the subject using the 3D poseestimation system 716. The one or more balance parameters predicted bythe one or more data processing devices 104 may comprise at least oneof: (i) a center of pressure, (ii) a center of mass, (iii) a center ofgravity, (iv) a sway angle, and (v) a type of balance strategy. Also,the one or more data processing devices 104 of the illustrativebiomechanical analysis systems 710, 730 may be further configured toprovide feedback to the subject regarding his or her balance based uponthe one or more predicted balance parameters of the subject determinedusing the 3D pose estimation system 716.

In one or more further illustrative embodiments, the biomechanicalanalysis systems 710, 730 may further include a sensory output deviceconfigured to generate sensory feedback for delivery to a system user.The sensory feedback may comprise at least one of a visual indicator, anaudible indicator, and a tactile indicator. For example, the sensoryoutput device may comprise one or more of the types of sensory outputdevices described in U.S. Pat. No. 9,414,784, the entire disclosure ofwhich is incorporated herein by reference.

In one or more further illustrative embodiments, using the principles ofinverse dynamics, the biomechanical analysis systems 710, 730 mayfurther map the energy flow of the subject performing a balance activityin the capture space. The forces and torques occurring at each joint inthe body may be determined by the kinematic positions and groundreaction forces (predicted and/or real) and mapped from the bodysegments and joints in contact with the force plate. Additionally, atemporal plausible physics algorithm may be used to correct for theinertia of the body segments from the previous body movements. Also, thebiomechanical analysis systems 710, 730 may automatically calculatejoint stresses using inverse dynamics. For example, the biomechanicalanalysis systems 710, 730 may automatically calculate the knee torque inone such application.

Although the invention has been shown and described with respect to acertain embodiment or embodiments, it is apparent that this inventioncan be embodied in many different forms and that many othermodifications and variations are possible without departing from thespirit and scope of this invention. In particular, while an interactiveairplane game is described in the embodiment described above, those ofordinary skill in the art will readily appreciate that the invention isnot so limited. For example, as illustrated in the screen image 206 ofFIG. 15, the immersive virtual reality environment 208 couldalternatively comprise a scenario wherein the subject 204 is walkingalong a bridge 207. Also, the interactive game could involve navigatingthrough a maze, walking down an endless grocery aisle, traversing anescalator, walking down a path in the woods, or driving around a course.For example, an exemplary interactive driving game may comprise variousdriving scenarios. In the beginning of the game, the scenario maycomprise an open road on which the subject drives. Then, a subsequentdriving scenario in the interactive driving game may comprise drivingthrough a small, confined roadway tunnel. As such, the subject wouldencounter different conditions while engaging in the interactive drivinggame (e.g., a light-to-dark transition as a result of starting out onthe open road and transitioning to the confines of the tunnel), andthus, the interactive game would advantageously challenge various sensesof the subject. Of course, the interactive driving game could also beconfigured such that the subject first encounters the tunnel and then,subsequently encounters the open road (i.e., a dark-to-lighttransition). In addition, any other suitable game and/or protocolinvolving a virtual reality scenario can be used in conjunction with theaforedescribed force measurement system (e.g., any other interactivegame that focuses on weight shifting by the subject and/or a virtualreality scenario that imitates depth in a 2-D painting). As such, theclaimed invention may encompass any such suitable game and/or protocol.

Moreover, while reference is made throughout this disclosure to, forexample, “one embodiment” or a “further embodiment”, it is to beunderstood that some or all aspects of these various embodiments may becombined with one another as part of an overall embodiment of theinvention. That is, any of the features or attributes of theaforedescribed embodiments may be used in combination with any of theother features and attributes of the aforedescribed embodiments asdesired.

Furthermore, while exemplary embodiments have been described herein, oneof ordinary skill in the art will readily appreciate that the exemplaryembodiments set forth above are merely illustrative in nature and shouldnot be construed as to limit the claims in any manner. Rather, the scopeof the invention is defined only by the appended claims and theirequivalents, and not, by the preceding description.

The invention claimed is:
 1. A force measurement system, comprising: atleast one camera, the at least one camera configured to capture one ormore images of a scene that includes a subject; a force measurementassembly configured to receive the subject, the force measurementassembly including: a top surface for receiving at least one portion ofthe body of the subject; and at least one force transducer, the at leastone force transducer configured to sense one or more measured quantitiesand output one or more signals that are representative of forces and/ormoments being applied to the top surface of the force measurementassembly by the subject; and one or more data processing devicesoperatively coupled to the at least one camera and the force measurementassembly, the one or more data processing devices configured to receivethe one or more signals that are representative of the forces and/ormoments being applied to the top surface of the force measurementassembly by the subject, and to convert the one or more signals intooutput forces and/or moments, the one or more data processing devicesfurther configured to predict one or more balance parameters of thesubject by performing the following steps: receiving the one or moreimages of the scene from the at least one camera; extracting featuresfrom the one or more images of the scene for providing inputs to atrained neural network; and determining the one or more balanceparameters of the subject using the output of the trained neuralnetwork.
 2. The force measurement system according to claim 1, whereinthe one or more data processing devices are further configured toprovide feedback to the subject regarding his or her balance based uponthe one or more predicted balance parameters of the subject determinedusing the trained neural network.
 3. The force measurement systemaccording to claim 1, wherein the one or more balance parameterspredicted by the one or more data processing devices using the trainedneural network comprise at least one of: (i) a center of pressure, (ii)a center of mass, (iii) a center of gravity, (iv) a sway angle, and (v)a type of balance strategy.
 4. The force measurement system according toclaim 1, wherein the at least one camera is part of a motion capturesystem, the motion capture system comprising a plurality of cameras, andthe plurality of cameras of the motion capture system being operativelycoupled to the one or more data processing devices.
 5. The forcemeasurement system according to claim 1, wherein the one or more dataprocessing devices are further configured to determine a plausibility ofthe pose of the subject on the force measurement assembly by using thetrained neural network.
 6. The force measurement system according toclaim 1, wherein the force measurement assembly is in the form of aninstrumented treadmill.
 7. The force measurement system according toclaim 1, wherein the force measurement assembly is in the form of aforce plate or a balance plate.
 8. The force measurement systemaccording to claim 1, further comprising a base assembly having astationary portion and a displaceable portion, the force measurementassembly forming a part of the displaceable portion of the baseassembly, and the force measurement system additionally comprising atleast one actuator operatively coupled to the one or more dataprocessing devices, the at least one actuator configured to displace theforce measurement assembly relative to the stationary portion of thebase assembly.
 9. The force measurement system according to claim 8,wherein the at least one actuator comprises a first actuator configuredto rotate the force measurement assembly about a transverse rotationalaxis and a second actuator configured to translate the displaceableportion of the base assembly that includes the force measurementassembly.
 10. The force measurement system according to claim 1, furthercomprising at least one visual display device having an output screen,the at least one visual display device configured to display one or moredisplay scenes on the output screen so that the one or more displayscenes are viewable by the subject; and wherein the one or more dataprocessing devices are configured to dynamically adjust one or morevisual elements in the one or more display scenes displayed on theoutput screen of the at least one visual display device based uponmovement characteristics of the subject.
 11. The force measurementsystem according to claim 1, wherein the one or more data processingdevices are further configured to quantify errors in one or more balancetasks performed by the subject on the force measurement assembly. 12.The force measurement system according to claim 11, wherein the one ormore balance tasks include dual tasks where the subject is standing onthe force measurement assembly while simultaneously performing a taskusing his or her upper body.
 13. The force measurement system accordingto claim 1, wherein the output of the trained neural network comprises athree dimensional pose of the subject; and wherein the one or more dataprocessing devices are configured to predict the one or more balanceparameters of the subject by performing the following further steps:generating one or more heatmaps using the trained neural network; andapplying a maximization function to the one or more heatmaps to obtainthe three dimensional pose of the subject in the scene.
 14. The forcemeasurement system according to claim 13, wherein the one or moreheatmaps generated by using the trained neural network comprise one ormore volumetric heatmaps.
 15. A force measurement system, comprising: atleast one camera, the at least one camera configured to capture one ormore images of a scene that includes a subject; a force measurementassembly configured to receive the subject, the force measurementassembly including: a top surface for receiving at least one portion ofthe body of the subject; and at least one force transducer, the at leastone force transducer configured to sense one or more measured quantitiesand output one or more signals that are representative of forces and/ormoments being applied to the top surface of the force measurementassembly by the subject; and one or more data processing devicesoperatively coupled to the at least one camera and the force measurementassembly, the one or more data processing devices configured to receivethe one or more signals that are representative of the forces and/ormoments being applied to the top surface of the force measurementassembly by the subject, and to convert the one or more signals intooutput forces and/or moments, the one or more data processing devicesfurther configured to predict one or more performance parameters of thesubject by performing the following steps: receiving the one or moreimages of the scene from the at least one camera; extracting featuresfrom the one or more images of the scene for providing inputs to atrained neural network; and determining the one or more performanceparameters of the subject using the output of the trained neuralnetwork.
 16. The force measurement system according to claim 15, whereinthe output of the trained neural network comprises a three dimensionalpose of the subject; and wherein the one or more data processing devicesare configured to predict the one or more performance parameters of thesubject by performing the following further steps: generating one ormore heatmaps using the trained neural network; and applying amaximization function to the one or more heatmaps to obtain the threedimensional pose of the subject in the scene.
 17. The force measurementsystem according to claim 16, wherein the one or more heatmaps generatedby using the trained neural network comprise one or more volumetricheatmaps.
 18. The force measurement system according to claim 15,wherein the one or more data processing devices are further configuredto determine a plausibility of the pose of the subject on the forcemeasurement assembly by using the trained neural network.